COMPARATIVE NITROGEN PARTITIONING AND WATER USE BY …

COMPARATIVE NITROGEN PARTITIONING AND WATER USE BY NATIVE

AND INTRODUCED GRASS COMMUNITIES IN

SOUTHERN ALBERTA, CANADA

by

Shane Warren Porter

A dissertation submitted in partial fulfillment of the requirements for the degree

of

Doctor of Philosophy

in

Land Resources and Environmental Sciences

MONTANA STATE UNIVERSITY Bozeman, Montana

August 2005

© COPYRIGHT

by

Shane Porter

2005

All Rights Reserved

ii

APPROVAL

of a dissertation submitted by

Shane Warren Porter

This dissertation has been read by each member of the dissertation committee and has been found to be satisfactory regarding content, English usage, format, citations,bibliographic style, and consistency, and is ready for submission to the College ofGraduate Studies.

Dr. Jon M. Wraith

Approved for the Department of Land Resources and Environmental Science

Dr. Jon M. Wraith

Approved for the College of Graduate Studies

Dr. Joseph J. Fedock

iii

STATEMENT OF PERMISSION TO USE

In presenting this dissertation in partial fulfillment of the requirements for a

doctoral degree at Montana State University–Bozeman, I agree that the Library shall

make it available to borrowers under rules of the Library. I further agree that copying of

this dissertation is allowable only for scholarly purposes, consistent with "fair use" as

prescribed in the U.S. Copyright Law. Requests for extensive copying or reproduction of

this dissertation should be referred to Bell & Howell Information and Learning, 300

North Zeeb Road, Ann Arbor, Michigan 48106, to whom I have granted "the exclusive

right to reproduce and distribute my dissertation in and from microform along with the

non-exclusive right to reproduce and distribute my abstract in any format in whole or in

part."

Shane Warren Porter

August, 2005

iv

ACKNOWLEDGMENTS

I would like to thank my major advisor at Montana State University, Dr. Jon

Wraith, and my advisor at the Lethbridge Research Center, Agriculture and Agrifood

Canada, Dr. Walter Willms, for the ideas, support, and encouragement they have given

me as a graduate student at Montana State University–Bozeman.

I would also like to thank the other members of my graduate committee, Dr. Paul

Hook, Dr. Jerry Nielsen, Dr. Clayton Marlow, and Dr. David Weaver for their assistance.

I could not have accomplished this without the help of Marj Scheurokogel and

Paula Dressler who assisted in the word-processing and formatting of this dissertation.

My special thanks go to the following researchers at the Lethbridge Research

Center: Dr. Chi Cheung, Dr. Henry Janzen, Dr. Ben Ellhert, and Toby Entz. I would also

like to thank Ryan Beck, Dan Hoover, Harriet Douwes, Rosie Wallender, Emily Davies,

and Mari Henry for their help with laboratory work.

I am especially grateful to Dr. Johann Dormaar who told me the story of grassland

soils and was always willing to listen and discuss.

Finally, I would like to give special thanks to my wife, mom, and family for their

loving support.

v

TABLE OF CONTENTS

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2. LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Plant Community Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Cultivation and Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Cultivation and Water Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3. NITROGEN PARTITIONING IN NATIVE AND AGRONOMIC COMMUNITIES IN THE NORTHERN GREAT PLAINS . . . . . . . . . . 27

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Site Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Site and Year Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Biomass and Root: Shoot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Nitrogen Concentration in Roots and Shoots . . . . . . . . . . . . . . . . . . . 39Total Nitrogen in Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Native Grassland Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Annual Monocultures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Perennial Monocultures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

vi

TABLE OF CONTENTS - (Continued)

4. SOIL NITROGEN PARTITIONING IN NORTHERN GREAT PLAINS GRASSLANDS: SHORT-TERM RESPONSE TO AGRONOMIC TREATMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55


Site Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Soil Nitrogen Determination Methods . . . . . . . . . . . . . . . . . . . . . . . . . 57

Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

5. WATER UPTAKE RESUMPTION FOLLOWING SOIL DROUGHT: A COMPARISON BETWEEN NATIVE AND AGRONOMIC COMMUNITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76


Description of Source Material Sites . . . . . . . . . . . . . . . . . . . . . . . . . . 78Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

Water Uptake Following Periods of Drought . . . . . . . . . . . . . . . . . . . . 84Differences in the Rate of Water Uptake After Drought . . . . . . . . . . . 86

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

6. COMPARATIVE WATER USE EFFICIENCY OF SELECTED NATIVE AND AGRONOMIC GRASS COMMUNITIES . . . . . . . . . . . 93


vii

TABLE OF CONTENTS - (Continued)

Site Description of Source Plant Material . . . . . . . . . . . . . . . . . . . . . . 94Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Environmental Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Above Ground Water Use Efficiency (Above Ground WUE) . . . . . . 97Crown and Root Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101The Effect of Water Content on Roots, Crowns and Above Ground Water Use Efficiency . . . . . . . . . . . . . . . . . . . . . . 101Above Ground WUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104References Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

7. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118

APPENDIX A: NITROGEN PARTITIONING TABLES IN CHAPTER 3 . . . 119

APPENDIX B: NITROGEN PARTITIONING TABLES IN CHAPTER 4 . . . 130

viii

LIST OF TABLES

Table Page

3.1 Monthly growing season precipitation (mm) and temperatures (°C) from 1995 to 1997 at three Southern Alberta Sites . . . . . . . . . . . . . . . . 30

3.2 Total model for total biomass, shoot mass, root mass, root: shoot (R:S),concentration N in shoot mass, concentration N in root mass, shoot mass N, root mass N. total N in biomass and R:S N of native and agronomic communities at three southern Alberta sites in 1995 and 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

4.1 Monthly precipitation (mm) over the growing season from 1995 to 1997 at three sites in southern Alberta . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.2 Total model for total soil nitrogen, mineralizable nitrogen, C:N in soil,ammonium (NH4

+), nitrate (NO3-), light fraction (LF), and total light

fraction nitrogen at three southern Alberta sites in 1995 and 1997 . . . . . . . 62

5.1 Linear regression slope of change in soil water content for six 7-day re-wet sequences from Day 210 to 295 of 1998 in crested wheatgrass, Russian wildrye, and needle-and-thread - blue grama grass communities planted in columns in a controlled-environment greenhouse at Montana State University, Bozeman, MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

5.2 Water uptake rates (mm h-1) for six 7-day re-wet sequences from Day 210 to 295 of 1998 in crested wheatgrass, Russian wildrye, and needle-and-thread - blue grama grass communities planted in columns in a controlled-environment greenhouse at Montana State University, Bozeman, MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

6.1 Long-term average, 1998, and 1999 monthly air temperature, relative humidity, wind speed, precipitation and Class A Pan evaporation over the growing season at the Lethbridge Research Centre rainout shelter in southern Alberta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

6.2 Table of fixed effects for dry weight, total water used and water use efficiency for the lysimeter study of needle-and-thread - wheatgrass - blue grama grass., crested wheatgrass, and Russian wildrye communities in soil with two different volumetric water contents in 1998 and 1999 . . . . 99

ix

LIST OF TABLES - (Continued)

Table Page

6.3 Dry matter production (g), total water use (kg) and water use efficiency (g kg -1) in native (needle-and-thread grass - wheatgrass - blue grama grass), crested wheatgrass, and Russian wildrye communities in 1998 and 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

6.4 Total root mass and root mass for 0-15 cm, 0-45 cm, and 45-90 cm depths in native (needle-and-thread grass - wheatgrass - blue grama grass), crested wheatgrass, and Russian wildrye communities grown in a rain-out shelter under two soil moisture regimes at Lethbridge, Alberta, Canada, in 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . 100

6.5 Mass of crowns at two different soil water contents (2) in crested wheatgrass, Russian wildrye and native Mixed Prairie (needle-and-thread grass - wheatgrass - blue grama grass) grown in a rain-out shelter at the Lethbridge Research Centre, Lethbridge, Alberta, Canada in 1998-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

x

LIST OF FIGURES

Figure Page

3.1 Total biomass nitrogen of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment means (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.2 Root mass of agronomic and native communities at Stipa-Bouteloua,Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment means (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.3 Shoot mass of agronomic and native communities at Stipa-Bouteloua,Stipa-Agropyron-Bouteloua and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.Error bars are standard error of the treatment population (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

3.4 Root-to-shoot ratio (R:S) of agronomic and native communities atStipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.Error bars are standard error of the treatment population (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.5 Nitrogen concentration in root mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua and

Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n = 8) . . . . . . 41

3.6 Nitrogen concentration in shoot mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are the standard error of treatment populations (n = 8) . . . . . 42

3.7 Total biomass nitrogen of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . 43

xi

LIST OF FIGURES - (Continued)

Figure Page

3.8 Total nitrogen in shoot mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.9 Total nitrogen in roots of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.1 Light fraction (LF) concentrations in the upper 7.5 cm of agronomic and native communities in Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in 1995 and 1997. Error bars are the standard error of treatment means (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

4.2 Total nitrogen content of the light fraction (LFN) in the upper 7.5 cm ofagronomic and native communities at Stipa-Bouteloua (SB), Stipa-Agropyron-Bouteloua (SAB), and Festuca-Danthonia (FD) sites in 1995 and 1997. Error bars are the standard error of treatment means (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

4.3 Mineralizable N in the upper 15 cm of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in 1995 and 1997. Error bars are the standard error of treatment (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4.4 Nitrate content in the upper 15 cm of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in 1995 and 1997. Error bars are the standard error of treatment means (n = 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

5.1 Changes in soil water content during six rewetting sequences between Day 210 and 245 of 1998 at 7.5, 15, and 30 cm soil depths in crested wheatgrass, Russian wildrye, and needle-and-thread - blue grama grasscommunities grown in columns at the controlled-environment greenhouse at Montana State University, Bozeman, MT. . . . . . . . . . . . . . . . . . . . . . . . . 80

xii

LIST OF FIGURES - (Continued)

Figure Page

5.2 Changes in soil water content during the first two re-wetting sequences (re-wet 1 and 2) between Day 210 and 245 of 1998 at 7.5 and 15 cm soil depths in crested wheatgrass, Russian wildrye, and needle-and-thread - blue grama grass communities grown in columns at the controlled-environment greenhouse at Montana State University, Bozeman, MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

5.3 Changes in soil water content during the second two re-wetting sequences (re-wet 3 and 4) between Day 245 and 275 of 1998 at 7.5 and 15 cm soil depths in crested wheatgrass, Russian wildrye, and needle-and-thread - blue grama grass communities grown in columns at the controlled-environment greenhouse at Montana State University, Bozeman, MT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

xiii

ABSTRACT

The objectives of this research were to evaluate 1) short-term changes in soil andplant N partitioning created by cultivating and re-seeding native grasslands with twocropping systems of wheat and perennial (crested wheatgrass and Russian wildrye)monocultures; 2) differences in the rate of soil water uptake between Mixed Prairiegrasslands, crested wheatgrass and Russian wildrye after a dry-down period; and 3)differences in above ground water use efficiencies, root and crown masses betweenMixed Prairie grasslands, crested wheatgrass and Russian wildrye under two differentsoil water contents. The perennial agronomic species were recommended by Agricultureand Agrifood Canada for seeding in Mixed Prairie and Fescue grassland in southernAlberta, Canada. In the first four years after plow-down, soil nitrate (NO3

-) concentrationwas higher and light fraction N (LFN) was lower in the soil under wheat than nativegrasslands. Although LFN was lower in perennial monocultures than native grasslands,there was little difference in soil nitrate. More N was partitioned into shoot biomass ofwheat, crested wheatgrass and bromegrass that native grasslands and levels increased asannual and long-term growing season precipitation increased. There were no differencesin the rate of soil water uptake after dry-down periods between native Mixed Prairie,crested wheatgrass or Russian wildrye, but both perennial monocultures had higher aboveground water use efficiencies than native Mixed Prairie.

1

1The names of some of the grasses in these communities have been revised, but the communities themselves have not been renamed.

CHAPTER 1

INTRODUCTION

Over 60% of the 114 million acres of the Northern Great Plains occur in Canada

(Padbury et al. 2002), with a majority being found on an eastward sloping plain between

the Rocky Mountains and the Precambrian Shield. The zonal climate of this northern

grassland is marked by low growing season precipitation, high winds, and drought, with

differences in amount, pattern, variability, intensity, and duration of precipitation

determining the size and species composition of each plant association. Although five

associations occur in the Canadian Northern Great Plains, only Mixed Prairie, Fescue

Prairie, and Parkland are found in Alberta (Smoliak et al. 1976).

In the Mixed Prairie association of southcentral and southeastern Alberta, a lack

of relief coupled with a variable dry-subhumid to semi-arid climate and the presence of a

Chernozemic soil allows the co-existence of mid and short-grass species (Clements 1920,

Coupland 1992a). This association can be further divided into five vegetation types1:

Agropyron-Koelaria, Bouteloua-Agropyron, Stipa-Agropyron, Stipa-Bouteloua and

Stipa-Agropyron-Bouteloua. The first two vegetation types are primarily edaphic

climaxes; the Agropyron-Koelaria vegetation type occurs on soils originating from

lacustrine clay deposits and the Bouteloua-Agropyron vegetation type has underlying

2

shale and a Solonetzic character to the soil. The Stipa-Bouteloua and Stipa-Agropyron-

Bouteloua vegetation types occur in loamy soils with differences in soil and species

composition primarily the result of differences in long-term average annual precipitation.

The Stipa-Bouteloua community in southeastern Alberta exists on the Brown subgroup of

the Chernozemic order (Aridic Ustochept) with a long-term average annual precipitation

near 33 cm, while the Stipa-Agropyron-Bouteloua community of southcentral Alberta

occurs on Dark Brown subgroups of the Chernozemic order (Typic Haploboroll) with an

average annual precipitation near 40.2 cm. Both of the above vegetation types are

affected by high evaporation which leads to precipitation-to-evaporation ratios between

0.3 and 0.5. The final vegetation type in the Mixed Prairie is Stipa-Agropyron which is

thought to be a transition between Mixed Prairie and Fescue Prairie (Smoliak et al. 1976).

In Alberta, Fescue Prairie is restricted to the north and northwest fringe of the

Northern Great Plains in the lower southern foothills of the Rocky Mountains (Strong

1992) where the large bunchgrasses Festuca campestris Rydb. (rough Fescue) and

Danthonia parryi Scrib. (Parry’s oatgrass) are dominant (Moss 1944). In this grassland

the climate is sub-humid, and the soils are classified as Orthic Black Chernozemic soils

(Udic Haploboroll). The average annual precipitation is 55 cm, with a precipitation-to-

evaporation ratio approximating 1.0, and less than 170 growing season days (Coupland

1961, Naeth et al. 1991). Although precipitation is higher in this association than in the

Mixed Prairie, the increase in the precipitation-to-evaporation ratio is primarily a result

of lower evaporation due to the higher altitude which results in a lower annual

temperature (Hart et al. 1995).

3

In the pre-European settlement period in Canada, stable prairie ecosystems

existed, with decomposition of plant residues resulting in the accumulation of soil

organic matter (SOM) and a stable pool of nutrients for the plant growth. In addition,

SOM increased aggregation in the soil, which, in turn, increased infiltration and storage

of water and decreased erosion. Prior to settlement, the primary disturbances affecting the

Canadian portion of the Northern Great Plains were fire and bison grazing.

In the late nineteenth and early twentieth century, the development of dry-land

farming techniques and mechanization accelerated the conversion of native grasslands to

annual crops and hayland (Johnston 1981). A prolonged depression and drought that

occurred in the second decade of the twentieth century left approximately 650,000

hectares of abandoned land bare, causing large amounts of soil erosion and weed

infestation. Research found that most of these problems could be controlled by strip

farming, stubble retention, and/or establishing perennial grasses such as Agropyron

cristatum (L.) Gaertn. (crested wheatgrass) and Psathyrostachs juncea (Fisch.) Nevski

(Russian wildrye) (Dormaar and Smoliak 1985). These introduced grasses establish

quickly, consistently yield more than native range, and control a variety of annual and

perennial weeds (Westover and Rogler 1934, Reitz et al. 1936, Pavylchenko 1942, Hull

and Stewart 1948, Hubbard 1949, Hull and Klomp 1966, Smoliak et al. 1967, Springfield

and Reid 1967, Smoliak 1968, Currie 1970, Looman and Heinrichs 1973, Smoliak and

Slen 1974, Dormaar et al. 1978, Dormaar et al. 1980, Smoliak and Dormaar 1985). Once

established, pastures of these species have remained productive for more than fifty years

as monocultures due to their ability to resist invasion by other species (Smoliak et al.

4

1967, Valentine 1971, Looman and Heinrichs 1973, Dormaar et al. 1978, Call and

Roundy 1991).

In the late 1960s, another wave of “sod-busting” or “plow-down” began in

Alberta grasslands despite concerns that the experience of the thirties had shown that

marginal semiarid land in southeastern Alberta could not economically sustain

agriculture over the long term. In addition, an increasing number of acres of mesic

Fescue grasslands were being plowed and replaced by annual cereal crops and cultivars

of introduced perennial forage grasses, such as Bromus inermis Leyss. (smooth brome

grass) and Dactylis glomerata L. (orchardgrass) (Suleiman et al. 1999).

Eventually, over 75% of the western Canadian native grasslands were replaced

with annual crops or perennial forages of which approximately 55 million hectares

seeded to annual cereal and seed crops. Of that 55 million hectares, over 50% is cropped

in wheat (Canadian Wheat Board 2002) and 12% in perennial forages. Of the area

planted to forages, approximately one million hectares is crested wheatgrass, and one

hundred thousand hectares is Russian wildrye (Johnston et al. 1986, Dormaar et al.1980,

Smoliak and Dormaar 1985, Statistics Canada 1999). The remaining native prairie is

either too dry or too rough to make cultivation economical at this time (Willms et al.

1993).

However, with global human population growing exponentially, the demand for

food will be used to justify conversion of the remaining native grasslands. Coupland

(1979a) and Heady and Child (1994) believe it is urgent to obtain a greater understanding

of the mechanisms and processes that control various native grassland ecosystem

5

components, including the capture and flow of energy and nutrient cycles such carbon,

nitrogen, and phosphorous, since they are pivotal in sustaining grassland ecosystem

function.

In the past, as native grasslands were replaced with agronomic systems, over-

simplification of natural systems, poor interpretation of knowledge, and the need for

quick results meant a loss of economic sustainability (Costello 1957, Heady and Child

1994). Although in the short term, replacement generally increases yields of both annual

cereals and forage crops, it is likely due to changes in ammonification, nitrification, and

water use (Johnston et al. 1986). However, more baseline information is needed to better

understand both the changes and the rate of change immediately following cultivation.

This project was initiated to investigate changes in nitrogen partitioning and water

dynamics in the first few years after plowing and seeding native grasslands in southern

Alberta Canada to annual and perennial agronomic species. The objectives of this study

were to determine 1) short-term changes in soil N partitioning created by the cultivating

and seeding native grasslands with selected annual (wheat) and perennial (crested

wheatgrass and Russian wildrye) monocultures; 2) changes in biomass partitioning of N

within these communities; 3) difference in the rate of water uptake between Mixed

Prairie grasslands, crested wheatgrass and Russian wildrye after a period of water stress;

and 4) differences in above ground water use efficiencies, root and crown masses

between Mixed Prairie grasslands, crested wheatgrass and Russian wildrye at two

different soil water content. It is hypothesized that above-ground production of seeded

forages and cereals is greater than native grassland communities in the first few years

6

after “plow-down.” During that period, the quality of the soil is expected to deteriorate

and will ultimately cause the system to be unsustainable. The rate of uptake after a period

of water stress of perennial communities (crested wehatgrass and Russian wildrye) will

be more rapid and water use efficiency will be greater allowing these agronomic

communities to access and assimilate more soil nitrogen.

7

References Cited

Call, C.A. and R.A. Roundy. 1991. Perspectives and processes in revegetation of arid andsemiarid rangelands. Journal of Range Management 44:543-549.

Canadian Wheat Board. 2002. www.cwb.ca.

Clements, F.E. 1920. Plant indicators: the relationship of communities to process andpractice. Carnegie Institute Washington Publication 290. 388 p.

Costello, D.F. 1957. Application of ecology to range management. Ecology 38:49-53.

Coupland, R.T. 1961. A recondieration of grassland classification in the Northern GreatPlains of North America. Journal of Ecology 49:135-167.

Coupland, R.T. 1979a. Background. In: R.T. Coupland (ED.). Grassland ecosystems ofthe world: analysis of grasslands and their uses. Cambridge, Great Britain:Cambridge University Press. p. 3-22.

Coupland, R.T. 1992a. Mixed prairie. In: R.T. Coupland (ED.). Ecosystems of the world8A: natural grasslands - introduction and western hemisphere. New York, NY:Elsevier. 469 p.

Currie, P.O. 1970. Influence of spring, fall and spring-fall grazing on crested wheatgrassrange. Journal of Range Management 23:103-108.

Dormaar, J.F., A. Johnston, and S. Smoliak. 1978. Long term soil changes associatedwith seed stands of crested wheatgrass in Southern Alberta, Canada. In: Proc. 1stInternational Rangelands Congress. Denver, CO: Society for Range Managment.p. 623-625.

Dormaar, J.F., A. Johnston, and S. Smoliak. 1980. Organic solvent-soluble organicmatter from soils underlying range and crested wheatgrass in southeasternAlberta, Canada. Journal of Range Management 33:99-101.

Dormaar, J.F., and S. Smoliak. 1985. Recovery of vegetative cover and soil organicmatter during revegetation of abandoned farmland in a semiarid climate. Journalof Range Management 38:487-491.

Hart, R.H., W.D. Willms, and M.R. George. 1995. Cool-Season Grasses in Rangelands.Chapter 12. In: L.E. Moser (ED.). Cool-season forage grasses. Madison, WI:Agronomy Monographs #24.

8

Heady, H.F., and D. Child. 1994. Rangeland ecology and management. San Fransisco,CA: Westview Press.

Hubbard, W.A. 1949. Results of studies of crested wheatgrass. Science and Agriculture 29:385-395.

Hull, A.C., and G.J. Klomp. 1966. Longevity of crested wheatgrass in the sagebrushgrass type in southern Utah. Journal of Range Management 19:5-11.

Hull, A.C., and G. Stewart. 1948. Replacing cheatgrass by reseeding with perennialgrasses on southern Idaho range. Journal of American Society of Agronomy40:694-703.

Johnston, A. 1981. History of agriculture in the prairie region of western Canada.Director’s Work- Planning Meeting. Agriculture Research Station. Lethbridge.

Johnston, A., Dormaar J.F., and S. Smoliak. 1986. The regrassing of southeasternAlberta. The Palliser Triangle: Interdisciplinary Studies of the Alberta,Saskatchewan and Montana Borderlands. May 15-18, 1986. Medicine Hat, AB:11 p.

Looman, J., and D.H. Heinrichs. 1973. Stability of crested wheatgrass pastures underlong-term pasture use. Canadian Journal of Plant Science 53:501-506.

Moss, E.H. 1944. The prairie and associated vegetation of southwestern Alberta, Canada.Journal of Resources C22:209-227.

Naeth, M.A., A.W. Bailey, D.S. Chanasyk, and D.J. Pluth. 1991. Water holding capacityof litter and soil organic matter in Mixed Prairie and Fescue grassland ecosystemsof Alberta. Journal of Range Management 44(1):13-17.

Padbury, G., S. Waltman, J. Caprio, G. Coen, S. McGinn, D. Mortenson, J. Nielson, andR. Sinclair. 2002. Agroecosystems and Land Resources of the Northern GreatPlains Agronomy Journal 94:251-261.

Pavylchenko, T.K. 1942. The place of crested wheatgrass, Agropyron cristatum L. incontrolling perennial weeds. Science and Agriculture 22:459-460.

Reitz, L.P. M.A. Bell, and H.E. Tower. 1936. Crested wheatgrass in Montana. MontanaState College Agriculture Experimental Station Bulletin 323. 53 p.

Smoliak, S. 1968. Grazing studies on native range, crested wheatgrass and Russianwildrye pastures. Journal of Range Management 21:44-50.

9

Smoliak, S., and J.F. Dormaar. 1985. Production of Russian wildrye and crestedwheatgrass and their effect on prairie soils. Journal of Range Management38(5):403-405.

Smoliak, S., A. Johnston, M.R. Kilcher, and R.W. Lodge. 1976. Management of prairierangeland. Publication 1425. Ottawa, ON: Information Division, Department ofAgriculture. 30 p.

Smoliak, S., A. Johnston, and L.E. Lutwick. 1967. Productivity and durability of crestedwheatgrass in southeastern Alberta. Canadian Journal of Plant Science 47:539-547.

Smoliak, S., and S.B. Slen. 1974. Beef production on native range, crested wheatgrassand Russian wildrye pastures. Journal of Range Management 27:433-436.

Springfield, H.W., and E.H. Reid. 1967. Crested wheatgrass for spring grazing innorthern New Mexico. Journal of Range Management 20:406-408.

Statistics Canada. 1999. Table of seeded acres of cereal and forage crops in Canada in1999. http://cansim2.statca.ca/

Strong, W.L. 1992. Ecoregions and ecodistricts of Alberta. Volume 1. Edmonton, AB:Alberta Forestry, Lands and Wildlife.

Suleiman, A., E.K. Okine, L.A. Goonewardene, P.A. Day, B. Yaremcio, and G. Recinos-Diaz. 1999. Yield and feeding of prairie grasses in east-central Alberta. Journal ofRange Management 52(1): 75-82.

Valentine, J.F. 1971. Range development and improvements. Provo, UT: Brigham YoungUniversity Press. 545 p.

Westover, H.L., and G.A. Rogler. 1934. Crested wheatgrass. U.S.D.A. Leaflet 104.(revised 1947). 8 p.

Willms, W.D., S.M. McGinn, and J.F. Dormaar. 1993. Influence of litter on herbageproduction in the Mixed Prairie. Journal of Range Management 46(4):320-324.

10

CHAPTER 2

LITERATURE REVIEW

Plant Community Dynamics

The process by which assemblages of plant species develop into long-lived stable

communities in specific environments has been debated since Clements (1916) first

developed the climate climax theory. In the last 30 years, a synthesis of ideas relating to

community stability has emerged among such diverse fields as ecophysiology, soil

organic matter dynamics, herbivory, plant competition, and fire ecology, in which a

discussion of vegetation-soil feedbacks in grassland ecology is central.

Tilman (1987a) suggested that a mechanistic approach to grassland ecology

would allow the development of this concept and move away from the rather

deterministic view put forth by Clements. This approach would define species

performance in terms of demography (including patterns of recruitment and mortality),

resource use efficiency, and partitioning, under specific environmental conditions such as

water, nutrient and light availability, herbivory, and disturbance. Within the performance

criteria, linkages between nitrogen cycling, soil organic matter dynamics, and plant

nitrogen use are fundamental (Tilman 1988, Wedin 1999). In most ecosystems, it is

assumed that the dominant plant species control ecosystem processes such as

productivity and nutrient cycling (Schlesinger 1996); however, recent studies have

11

addressed a range of ecosystem characteristics including the diversity of plant species

and functional characteristics of individual species (Tilman et al. 1997, Hooper and

Vitousek 1998, Hector et al. 1999, Knops et al. 2001, Loreau et al. 2001). The functional

characteristics of the component species in any ecosystem are likely to be at least as

important as the number of functional groups present for maintaining critical ecosystem

processes and services (Hooper and Vitousek 1997).

Plant species adapted to temporary, highly variable and uncrowded environments

as occur after disturbance have different life histories than those found in stable, crowded

environments. The former have short life spans (annual or biennial), rapid

photosynthetic, respiratory, transpiratory, growth, and reproductive rates, relatively low

root:shoot ratios (R:S), rapid responses to changes in environmental resources, and high

acclimation and dispersal ability. In most native grassland communities, a majority of the

species are stable assemblages of perennial species. These species are capable of

withstanding competition, possess slow growth and low reproductive rates, and direct

more resources into organs that will guarantee survival over the long term (e.g., higher

R:S) (Bazzaz 1986, Brewer 1988). Once these communities are disturbed, succession

may depart from the expected outcomes proposed by classical Clementsian theory (Ellis

and Swift 1988, Behnke et al. 1993) due to discontinuous irreversible changes associated

with most disturbances (Holechek et al. 1998). Cultivation of native grasslands causes

physical, chemical, and biological changes in the soil, as well as altering the plant

community such that feedbacks between existing soil characteristics and newly

introduced plant species may prevent the redevelopment of the original community when

12

cultivation ceases (Vinton and Burke 1995). Changes in productivity and R:S ratios may

change the quality and quantity of N partitions in the soil.

Cultivation and Nitrogen

Both natural and agricultural ecosystems provide many services and goods that

are essential for food and a range of other products that support our existence (Matson et

al. 1997). A burgeoning global human population has created an increased need for the

production of food, and increasing agricultural intensification is resulting in a reduction

of diversity, with large areas of monoculture cropping made up not only of identical crop

species, but individuals with the same genetic code (Dearden and Mitchell 1998).

Since the beginning of the twentieth century, improved agricultural technologies

such as mechanization, irrigation, molecular genetics, fertilizers, and pesticides have

increased yields dramatically. In these systems, the dominant role taken by farmers in the

modifying of the abiotic environment, selection of organisms planted, and control of

species that reduce production represents a cost to the rest of the ecosystem in terms of

energy, matter, and biological diversity. These changes do not necessarily result in the

impairment of ecosystem services unless diversity-function thresholds are breached by

the elimination of key functional groups, species, or organisms (Swift et al. 2004).

Tillage and seeding of the landscape and changes of native grasslands causes

massive modifications in the structural and functional diversity of communities and

ecosystems. These activities introduce species with differences in lifespan, growth form,

biomass allocation, and tissues chemistry than existed in the original community.

13

Changes also include modification in soil structure, bulk density chemistry, thermal and

hydraulic properties, aggregation, quantity and quality of SOM, N, water retention and

soil microbial and macrobial populations (Griffiths and Burns 1972, Dormaar et al. 1978,

Jenny 1980, Dormaar et al. 1990). All of these changes can have significant impacts on

critical ecosystem processes that promote stability and sustainability.

In the past, dryland agriculture on the Canadian prairies has concentrated on the

production of cereals, oil seeds, and forages. In 2004, cereal species represented the

greatest acreage planted on the Canadian Northern Great Plains, with over 10.3 million

hectares planted to wheat (Statistics Canada 1999). By 1986, 2.5 million hectares of

perennial forage pastures were utilized by the beef industry in the prairie provinces, with

over 1 million in crested wheatgrass and Russian wildrye (Smoliak and Dormaar 1985).

Domestic cereal crops are annual species that have high photosynthetic,

respiration, transpiration, growth and reproductive rates, low root:shoot ratios and highly

viable seeds (Mooney 1972, Newell and Tramer 1978, Bazzaz 1986, Brewer 1988), and

only maintain their dominance through anthrogenic activites such as tillage and

fertilization. These species quickly colonize the new readily-available nitrogen pool

within their rooting zone but may rapidly reduce this N pool. Numerous studies with

wheat have demonstrated reductions in SOM over time, as a function of cropping system,

crop rotation, tillage, and other agronomic factors (Campbell et al. 1990, Janzen et al.

1992). Of particular concern is the loss in labile organic matter, which plays a prominent

role in soil nutrient dynamics and appears to be more susceptible to short-term cropping

practices (Campbell and Souster 1982, Parton et al. 1987, Janzen 1987, Skjemstad et al.

14

1998, Janzen et al. 1992). At some point, without the addition of fertilizer, available soil

N becomes insufficient to support high above-ground biomass production (Redente et al.

1992).

In the last 60 years, perennial grasses have been introduced into the Canadian

northern Great Plains to prevent erosion of abandoned land or to improve land to allow

an increase in beef production (Smoliak et al. 1967). The four prominent species seeded

in these grasslands are crested wheatgrass, Psathyrostachs juncea (Fisch.) Nevski

(Russian wildrye), Dactylis glomerata L. (orchardgrass) and Bromus inermis Leyss.

(smooth bromegrass). The first two species are recommended by Agriculture and

Agrifood Canada for drier Mixed Prairie grasslands and the latter for more moist Mixed

Prairie and Fescue grasslands. Once these grasses are seeded, they tend to become a

permanent part of the landscape (Smoliak et al. 1967).

Crested wheatgrass is tolerant of cold and drought, establishes quickly, is

outstanding in early season production and nutritive value (Knowles and Buglass 1966,

Smoliak at al. 1970, Knowles 1987, Looman and Heinrichs 1973). Redente et al. (1989)

and Christian (1996) reported 1.7 to 3 times greater above-ground biomass with

monocultures of this species than for native grass in Saskatchewan. Although the N

content of the standing crop of crested wheatgrass is higher in the spring, by fall it was

1.01% (Lawrence 1978) due to senescence and N translocation to crowns and roots. The

root mass of crested wheatgrass was between 60 and 71% of the native Stipa-Boutleoua

community (Smoliak et al. 1967, Dormaar et al. 1978, Christian 1996). Russian wildrye,

due to later development, maintains forage quality into the fall. Smoliak and Dormaar

15

(1985) found that over a 25-year period, this species produced 47% more forage than

native grasslands. Smooth bromegrass and orchardgrass are often seeded on soils that are

mildy acidic and/or poorly drained. Bromegrass spreads quickly by rhizomes and

produces higher dry matter yields than orchardgrass. In southwestern Saskatchewan and

nothern Montana, Lawrence (1978), Knowles (1987), and Wickman (1998) found that

varieties of bromegrass have high yields, with between 1.44 and 1.68% N in standing

crop during the fall but protein levels in orchardgrass remain higher (Couleman 1987,

Tannas 1991). Orchardgrass dry matter production is better distributed over the growing

season and is the most competitive of the two species (Couleman 1987, Tannas 1991).

The competitive ability of orchardgrass may be due to its early spring growth and the

presence of many basal leaves (Jung and Baker 1984).

Cultivation and Water Relations

Vast regions of native grasslands experience water stress due to limited

precipitation during the growing season. This lack of moisture may modify nutrient

acquisition, photosynthetic activity and growth, and cause damage in the plant and/or

intensify competition between plants and influence feedback systems that control

ecosystem (Kramer 1980, Swindale and Bidinger 1981, Wedin and Tilman 1990, Brown

1995, Vila and Sardans 1999). The physiological consequences of water deficits differ

with species, type of plant, current environmental conditions. As duration and intensity of

the water deficit persist, changes in root:shoot ratios occur as a result of a slowing in leaf,

shoot and tiller development, and stimulates root growth at the expense of shoots (Sharp

16

and Davies 1979, Brown 1995). Therefore, in grassland research, it is important to study

both plant responses to variations in available water and adaptations to water deficits

(Kramer 1983). Changes in these processes and controlling feedbacks created by tillage

and seeding of annual and perennial monocultures may create the potential for alternate

stable states in vegetation-soil systems (Wedin and Tilman 1990).

A number of researchers contend that the ability of a species to be a successful

competitor is a function of more efficient use of resources such as water (Tilman 1988,

Goldberg 1990, Busch and Smith 1995, Davis et al. 1998, Li 1999, Tsialtas et al. 2001),

while others contend that increased competition is a result of less efficient use by non-

native grasses, resulting in an increase in water uptake and demand, which leaves less for

competing species (Davis et al. 1998, Gordon et al. 1999). Both of these strategies could

inhibit establishment, survival, and/or reproduction of native species (Blicker et al.

2003).

Water use efficiency is defined as either the amount of water consumed by a plant

in transpiration per unit gain in growth or biomass production, or as gain in biomass per

unit of water transpired. Species have variable rates of water use relative to biomass

production, atmospheric conditions (precipitation, vapor pressure deficits between the

plant and air, and wind), stage of plant development, and soil physical and chemical

properties (Stanhill 1986). Water use efficiency is not a fixed characteristic within each

species, but is of interest to plant physiologists, breeders, and range managers because it

is used to define interactions of water use and nutrient gain as they affect plant growth,

survival, and response to stress (Ehleringer et al. 1993, Kramer 1983, Brown 1995,

17

Kramer and Boyer 1995). Measurements of WUE in the field are often hampered by

variability in rainfall, and crop responses to soil type and to agronomic practices (Asseng

et al. 2001). Agronomic practices which change the canopy structure, soil structure, soil

N and energy dynamics, may modify production or water acquisition and WUE

(Claussen 2002, Frank 2003).

Sims and Singh (1978b) suggested that natural communities dominated by cool

season grasses (C3) that possess higher aerial production than those dominated by warm

season (C4) grasses have higher water use efficiencies. However, when C3 species are

compared to C4 species, the latter have higher water use efficiencies due to

photosynthetic and structural differences (Black 1971). In Mixed Prairie and Fescue

Grassland in the northern Great Plains, a large range in WUE exists between

communities due to large variations in precipitation and temperature (Sims and Singh

1978a) which agrees with work done by Vinton and Burke (1995), who suggested these

processes are not primarily limited by plant-mediated characteristics but by the supply of

water itself. Many studies have shown differences in water use efficiency between

species (Johnson et al. 1990, Johnson and Bassett 1991, Read et al.1992, Akhter et al.

2003, Blicker et al. 2003, Xue et al. 2003). An understanding of species and community

differences in soil-water-root relationships will enhance our ability to effectively manage

plant, soil, and water resources, weed infestation, and will allow the design of multi-crop

agro-ecosystems that fill more below-ground niches (Noy-Meir 1973, Grime 1994,

Sheley and Larson 1995, Wraith and Wright 1998).

18

Rapid recovery of species after drought may be facilitated by a variety of factors

including difference in root distribution, rapid root growth and hydraulic lift which may

enhance biochemical conditions, nutrient availability, microbial processes, and the

acquisition of nutrients by roots (Bittman and Simpson 1989, Caldwell et al. 1998). In

the native Stipa-Bouteloua community, most of the root system occurs in the upper 15 cm

due to the prevalence of blue grama grass; however, root systems of needle and thread

grass and western wheatgrass penetrate much deeper (Weaver 1958, Coupland and

Johnson 1965). The ability of blue grama grass to rapidly raise leaf water potential

following rainfall, regardless of the previous drought stress, increased water uptake by

surviving roots and rapid development of new extensive fine root systems allows more

efficient absorption of water made available during short intense convection storms while

needle and thread and western wheatgrass access water lower in the profile (Plummer

1943, Briske and Wilson 1977, Coyne and Bradford 1985, Lauenroth et al. 1987, Johnson

and Aguirre 1991). Both crested wheatgrass and Russian wildrye have coarser, deeper

root systems than the Stipa-Bouteloua community (Weaver 1958, Smoliak and Johnston

1980, Dormaar and Sauerbeck 1983, Smoliak and Dormaar 1985). These differences may

create differences in the rate of the uptake of water after drought.

19

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27

CHAPTER 3

NITROGEN PARTITIONING IN NATIVE AND AGRONOMIC COMMUNITIESIN THE NORTHERN GREAT PLAINS

Introduction

Plant species in a native grassland differ in their ability to utilize nutrients, and

these differences impact species composition and nutrient cycling within communities

and ecosystems (Wedin and Tilman 1990, Burke et al. 1997, Wedin 1999). Plasticity in

resource allocation within these species created by differences in growth habit,

production, root: shoot ratios, and nitrogen partitioning allows these species to survive

changes in physical environment and interspecific interactions (Mueller 1941, Weaver

1958, Odum 1968, Hartnett and Keeler 1995, Whitehead 1995).

In the last 100 years, the demand for cereal, oil and feed grains, and forage has

resulted in a large portion of Canadian grasslands being replaced with simplified

agronomic communities modified to maximize the amount of usable product with a large

proportion removed through harvest, grazing or a combination of both. These changes

modify nitrogen cycling within the plant-soil complex and impact sustainability of these

agronomic systems (Spedding 1971, Love 1972, Pate and Farquhar 1988, Dormaar et al.

1995). However, the rate of change in the quantity and quality of the N partitions

immediately after plow-down is not well understood. Therefore, a three-year study was

undertaken to examine changes in N partitioning within common agronomic communities

28

that had been created out of nature rangeland. The purpose was to test the hypothesis that

cultivation and replacement of native grasslands with agronomic monocultures results in

greater N allocation into shoot mass and lower allocation into root mass than in native

grassland communities.

Materials and Methods

Site Description

The study was conducted at three sites in southern Alberta (Onefour, Lethbridge,

and Stavely) distinguished by differences in native community, climate, and soil. The

Onefour site was located in southeast Alberta near Manyberries (49o 07' N, 110o 29' W).

The Orthic Brown Chernozemic soil (Aridic Haploboroll) underlies a Stipa-Bouteloua

community with an average annual precipitation of 332 mm. The Stipa-Agropyron-

Bouteloua site near Lethbridge in south-central Alberta (49o 43' N, 110o 57' W) possesses

an Orthic Dark Brown Chernozemic (Typic Haploboroll) and an average annual

precipitation of 402 mm (Smoliak et al. 1967, Ellert and Janzen 1999). The Fescue

Prairie grassland (Festuca-Danthonia) site was located in the Porcupine Hills west of

Stavely, Alberta (50o 12' N, 113o 57' W). The soil is an Orthic Black Chernozemic (Udic

Haploboroll) with an average annual precipitation of 493 mm (Dormaar and Willms

1993). The vegetation at these three sites has been described in detail by Moss (1944) and

Coupland (1961).

29

Weather records including precipitation and temperatures were obtained for the

period of the study reported herein from meteorological stations at Onefour, Lethbridge,

and Claresholm. Precipitation during the growing season (March to September) in 1995

at the Stipa-Bouteloua, Stipa-Agropyron-Bouteloua and Festuca-Danthonia sites were,

respectively, 148, 137, and 83% of the long term average (Table 3.1). In 1996, precipi-

tation at the Festuca-Danthonia and Stipa-Agropyron-Bouteloua sites was well below the

long-term average, but near the average at the Stipa-Bouteloua site (Table 3.1). In 1997,

all three sites experienced near average growing season precipitation (Table 3.1). Long-

term growing season temperatures (March through September) among sites were Stipa-

Bouteloua > Stipa-Agropyron-Bouteloua > Festuca-Danthonia site (Table 3.1). In 1995,

the Stipa-Bouteloua and Stipa-Agropyron-Bouteloua sites were approximately 2 and 4o C

lower than the long-term average, respectively, while the Festuca-Danthonia site was

approximately 4o C above normal. In 1997, the growing season temperatures at all three

sites was above the long-term average, with Stipa-Bouteloua, Stipa-Agropyron-Bouteloua

and Festuca-Danthonia sites being 7, 10, and 3o C higher, respectively (Table 3.1).

Experimental Design

The effects of cultivation and seeding were tested at each site by planting two

perennial grass monocultures recommended by Agriculture and Agrifood Canada, and

two cropping systems of Triticum aestivum L. ‘Katepwa’ (spring wheat), in a randomized

complete block design. Four replicates of five treatments were established in 3 x 10 m

plots with native grassland serving as a control. The treatments were imposed on three

30

Table 3.1. Monthly growing season precipitation (mm) and temperatures (ºC) from 1995 to 1997 at three southern Alberta sites.

Precipitation (mm)

Year March April May June July Aug. Sept. Total %1

Stipa-Bouteloua

1995 17 37 41 130 56 50 48 379 148

1996 32 13 64 80 33 4 51 277 109

1997 28 15 84 65 11 23 20 246 96

Ave. 2 22 28 41 64 34 39 27 255 100

Stipa-Agropyron-Bouteloua

1995 10 38 106 138 66 44 19 421 137

1996 21 22 54 18 5 70 6 196 64

1997 14 96 101 32 33 8 10 294 95

Ave. 2 24 31 55 74 42 42 40 308 100

Festuca-Danthonia 3

1995 6 23 72 84 69 39 63 356 83

1996 45 24 72 49 7 4 54 255 60

1997 15 21 138 73 28 77 35 387 91

Ave. 2 24 14 99 113 74 69 34 427 100

Mean Monthly Temperatures (ºC)


Stipa-Bouteloua

1995 -1.2 3.6 10.8 15.8 18.0 17.6 13.0 11.1 97.9

1997 -1.5 3.6 11.4 16.6 19.3 19.6 15.7 12.1 106.8

Ave. 2 -2.9 5.2 11.4 15.6 19.6 18.8 12.2 11.3 100.0


1995 -0.3 4.3 10.1 14.6 17.3 15.8 12.5 10.6 96.3

1997 0.7 3.9 11.3 16.0 18.2 18.6 15.9 12.1 109.7

Ave. 2 -1.5 5.6 10.8 14.9 18.0 17.1 12.2 11.0 100.0

Festuca-Danthonia3

1995 -1.4 3.7 9.2 14.1 16.1 15.0 11.9 9.8 104.4

1997 -2.0 2.0 8.8 12.9 15.5 16.3 14.3 9.7 103.2

Ave. 2 -2.1 5.0 8.7 12.8 15.7 15.2 10.4 9.4 100.0 1 % - Sum of precipitation or temperatures from March to September divided by the long-term averages during the same period 2 Averages over a 50-year period - Agriculture and Agrifood Canada 3 Measured at Claresholm which was approximately 30 m southeast of the study site

31

previously uncultivated native grassland sites that had been lightly grazed. The Stipa-

Agropyron-Bouteloua and Festuca-Danthonia sites were established in 1993, while the

Stipa-Bouteloua site was established in 1994. At the time of establishment, all sites were

protected from livestock grazing by fences. The perennial grasses seeded on Mixed

Prairie sites (Stipa-Bouteloua and Stipa-Agropyron-Bouteloua) were Agropyron

cristatum (L.) Gaertn. (crested wheatgrass) and Psathyrostachy juncea (Fisch.) Nevski

(Russian wildrye). On the Fescue prairie site (Festuca-Danthonia), the perennial grasses

seeded were Bromus inermis Leyss. (smooth bromegrass) and Dactylis glomerata L.

(orchardgrass ). At each site, two cropping systems were used with wheat; one treatment

was continuously cropped and the other was left fallowed alternate years. All seeding of

introduced grasses was done in the spring with 15-cm row spacing.

Methods

In 1995 and 1997, standing crop at each site was estimated by harvesting plant

biomass to a 2 cm stubble height in two randomly located 0.25-m2 subplots (0.5 x 0.5 m)

in each treatment and block. Net annual aerial production (shoot) was estimated by

removing standing litter from green standing crop. The plant material was oven-dried

(60o C) and weighed. Root biomass was sampled using three randomly placed cores (2

cm x 91 cm deep) in each treatment, and block using a hydraulic truck-mounted unit. The

samples were frozen until washed on a 2-mm screen over a 0.5-mm screen to remove

soil. The washed root samples were then oven-dried (60o C) and weighed.

32

Shoot and root mass samples were composited by treatment, ground with a

laboratory mill equipped with a 2-mm screen followed by a mill equipped with a 1-mm

screen. Approximately 8 mg subsamples were taken from each composite and analysed

for C and N using an automated dry combustion technique (Carlo Erba TM, Milan, Italy).

The ash content of the root samples was not determined; however, care was taken in the

washing of the roots to reduce differences due to the presence of soil.

Statistical Analyses

The dependent variables were analysed as a split-plot design with site, treatment,

and their interaction as the main plot effects, and time and its interactions with the other

factors as the split-plot effects (Steel and Torrie 1980). For these analyses, the two grass

and two wheat treatments were individually pooled and analysed in a whole model as an

unbalanced 3 (site) x 2 (years) x 3 (treatments) split-plot design, where the treatments

were native grass, agronomic grass, and wheat. This grouping was necessary to avoid the

nesting of treatments within sites. These analyses were performed to determine the

generalized effect of cultivating and seeding to perennial or annual grasses on production

and soil properties over a wide range of conditions. Separate split-plot analyses were also

performed for each site, with treatment as the main plot, and time and the time-by-

treatment interaction as the split-plot effects. Differences of means that were of interest

were evaluated for significance using single degree of freedom contrasts which are

reported in the appendices (Steel and Torrie 1980). All analyses of variance were

performed using the MIXED procedure from SAS (SAS Institute, Inc. 1999). Significant

33

differences between treatment means were determined as P< 0.05.

Results

Year, site, and treatment (with two grass and two wheat treatments pooled)

affected the magnitude of most variables (Table 3.2). Mass variables (biomass and N)

tended to follow the order: Stipa-Bouteloua < Stipa-Agropyron-Bouteloua < Festuca-

Danthonia, while the ratio of root to shoot mass and N concentrations in shoots tended to

follow the opposite order: Stipa-Bouteloua >Stipa-Agropyron-Bouteloua > Festuca-

Danthonia (Table 3.2). The effect of site on treatment for any variable tended to be

primarily on its relative magnitude rather than ranking within the site.

The effect of treatment on each variable was influenced by both site and year and,

in some cases, by their interaction (Table 3.2). Due to the complexity of interpretation,

the data was re-analysed by site to assess the effects of treatment (with two individual

grass and two individual wheat treatments) and year.

Site and Year Effect

Site affected the magnitude of all variables except N concentration in shoot mass

and influenced the effect of native pooled perennial grass and pooled wheat treatments on

all variables (Table 3.2). Nevertheless for any variable the effect of site on treatment

effects tended to be on magnitude rather than ranking treatments within each site. Year-

by-treatment interaction was significant for many variables at each site and there was

little consistency regarding significance among sites. Due to large numbers of significant

34

Table 3.2. Total ANOVA model for total biomass, shoot mass, root mass, root: shoot (R:S), concentration N in shoot mass, concentration N in root mass, shoot mass N, root mass N. total N in biomass and R:S N of native and agronomiccommunities at three southern Alberta sites in 1995 and 1997.

Biomass

(g m-2)

Shoot Mass

(g m-2)

Root Mass

(g m-2)

Root: Shoot Concentration Shoot N(mg g-1)

Concentration Root N(mg g-1)

Shoot N

(g m-2)

Root N

(g m-2)

Total N

(g m-2)

Source ----------------------------------------------------------------------------------------------------------Probabilities-------------------------------------------------------------------------------------------------Year (Y) 0.196 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.008Site (S) <0.001 <0.001 <0.001 0.015 0.070 0.031 <0.001 <0.001 <0.001Treatment (T) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001S x Y 0.552 0.003 0.179 0.114 <0.001 <0.001 0.030 0.077 0.085T x Y <0.001 <0.001 0.004 0.010 <0.001 0.006 <0.001 0.018 <0.001T x S <0.001 0.010 0.001 0.003 <0.001 <0.001 <0.001 <0.001 <0.001S x Y x T 0.384 0.005 0.674 0.228 <0.001 0.224 0.003 0.667 0.629Site -------------------------------------------------------------------------------------------------------------Means-----------------------------------------------------------------------------------------------------------Stipa-BoutelouaNative 1015.3 66.9 948.4 15.4 1.1 1.4 0.7 14.1 14.8Perennial Grass1 943.2 183.1 760.1 6.2 1.1 1.4 1.8 11.0 12.8Wheat2 987.8 503.9 483.9 1.2 0.7 1.6 3.8 8.1 12.0Stipa-Bouteloua-AgropyronNative 1135.7 181.2 1033.5 8.3 1.3 1.3 2.1 14.2 16.3Perennial Grass1 1152.9 203.3 1022.2 6.6 0.9 1.2 1.6 12.1 13.7Wheat2 809.7 524.2 306.4 1.1 0.8 1.6 3.8 5.1 8.9Festuca-DanthoniaNative 2153.2 265.0 1888.0 7.3 1.2 1.5 3.0 30.9 34.0Perennial Grass3 1731.1 389.9 1341.2 6.6 1.0 1.3 3.5 17.3 20.8Wheat2 1030.2 556.3 473.8 1.5 0.7 1.4 3.8 6.5 10.4

1 Crested wheatgrass and Russian wildrye.2 Fallow and continuously cropped wheat.3 Smooth bromegrass and orchardgrass.

35

year-by-treatment interactions and their inconsistencies, the means and differences

between means for each year, treatment, and site were determined and are reported in

appendices.

Biomass and Root: Shoot

There were few differences in total biomass between native grasslands and

perennial monocultures except for orchardgrass in 1997 (Figure 3.1). However total

biomass in native grasslands and perennial grasses was greater than wheat at each site

and year except at the Stipa-Bouteloua site in 1995 (Figure 3.1).

Root mass of native grasslands was greater than for wheat at all sites (Figure 3.2).

There were few differences in root mass between native grasslands and perennial species

except at the Stipa-Bouteloua and Festuca-Danthonia sites in 1997, where native

grasslands had a larger root mass than crested wheatgrass, Russian wildrye, and

orchardgrass (Figure 3.2).

In 1995 and 1997, native grasslands yielded less shoot mass than either wheat or

crested wheatgrass at the Stipa-Bouteloua site; however, the magnitude of the difference

was greater in 1995. A similar pattern was evident at the Stipa-Agropyron-Bouteloua

site; however, there was no difference in shoot mass of native grasslands and crested

wheatgrass in 1995 (Figure 3.3). In 1997, the native grassland shoot masses were similar

to those of perennial grasses on all sites (Figure 3.3), while wheat shoot mass was greater

than that of the native grasslands in both Stipa-Bouteloua and Stipa-Agropyron-

Bouteloua sites.

36

Figure 3.1. Total biomass nitrogen of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, andFestuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment means (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR -Russian wildrye, WC - wheat continuous crop, WF - wheat fallow.

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Treatment

NAT CWG RWR WC WF

Tota

l Bio

mas

s N

(g m

-2)

0

10

20

30

40

50

Tota

l Bio

mas

s N

(g m

-2)

0

10

20

30

40

501995 1995 1995

1997 1997 1997

Stipa-Bouteloua Stipa-Agropyron-Bouteloua Festuca-Danthonia

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Treatment

NAT CWG RWR WC WF

Roo

t Mas

s (g

m-2)

0

1000

2000

3000

Roo

t Mas

s (g

m-2)

0

1000

2000

3000

1997


1995 1995 1995

1997 1997

37

Figure 3.2. Root mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthoniasites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment means (n = 8). Symbols: B -brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russian wildrye, WC - wheatcontinuous crop, WF - wheat fallow.

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Treatment

NAT CWG RWR WC WF

Sho

ot M

ass

(g m

-2)

0

200

400

600

800

1000

1200

1400

Sho

ot M

ass

(g m

-2)

0

200

400

600

800

1000

1200

1400

1997

1995


1995 1995

1997 1997

38

Figure 3.3. Shoot mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.Error bars are standard error of the treatment population (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russian wildrye,WC - wheat continuous crop WF - wheat fallow.

39

In 1995 and 1997, native grasslands had greater root-to-shoot ratio (R:S) than all seeded

treatments in the Stipa-Bouteloua and Festuca-Danthonia sites with the exception of

orchardgrass (Figure 3.4). In 1997, Russian wildrye and native grasslands had similar

R:S in the Stipa-Agropyron-Bouteloua site (Figure 3.4).

Nitrogen Concentration in Roots and Shoots

Nitrogen concentration in shoot and root mass was affected by treatment in all

sites while year affected N concentration of shoot mass in Stipa-Bouteloua and Festuca-

Danthonia sites and root mass in the Stipa-Agropyron-Bouteloua site. N concentration in

root mass of fallow wheat was greater than that of native grasslands in both Stipa-

Bouteloua and Stipa-Agropyron-Bouteloua sites, while the root mass of the native

treatment had greater N concentration than perennial grasses in the Stipa-Agropyron-

Bouteloua site and only orchard grass in the Festuca-Danthonia site (Figure 3.5). In

Stipa-Bouteloua and Stipa-Agropyron-Bouteloua sites, the native treatment had a greater

N concentration in shoot mass than all other treatments except Russian wildrye (Figure

3.6). Similarly, the native treatment in the Festuca-Danthonia site had higher shoot N

concentrations than other treatments except orchardgrass (Figure 3.6).

Total Nitrogen in Biomass

Total N accumulated into biomass was greater in native grasslands than wheat,

crested wheatgrass and Russian wildrye at all sites at all sites in 1997 but only at the

Festuca-Danthonia site in 1995 (Figure 3.7). Wheat had greater N in shoot mass than

either native grassland or the perennial forages in 1995 except for Bromegrass

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

TreatmentNAT CWG RWR WC WF

Roo

t:Sho

ot R

atio

0

5

10

15

20

Roo

t:Sho

ot R

atio

0

5

10

15

20

Stipa-Bouteloua

1995

1997 1997

1995


1995

1997

Festuca-Danthonia

40

Figure 3.4. Root-to-shoot ratio (R:S) of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, andFestuca-Danthonia sites in southern Alberta in 1995 and 1997.Error bars are standard error of the treatment population (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russianwildrye, WC - wheat continuous crop WF - wheat fallow.

41

Figure 3.5. Nitrogen concentration in root mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.Error bars are standard error of thetreatment population (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - nativegrassland, RWR - Russian wildrye, WC - wheat continuous crop, WF - wheat fallow.

Treatment

NAT B O WC WF

N C

once

ntra

tion

(mg

kg -1

)

0

1

2

Treatment

NAT CWG RWR WC WF

N C

once

ntra

tion

(mg

kg -1

)

0

1

2

Treatment

NAT CWG RWR WC WF

Stipa-Bouteloua Stipa-Agropyron-Bouteloua

1997

1995

1997

1995

Festuca-Danthonia

1995

1997

42

Figure 3.6. Nitrogen concentration in shoot mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are the standard error oftreatment populations (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT -nativegrassland, RWR - Russian wildrye, WC - wheat continuous crop, WF - wheat fallow.


1995

N C

once

ntra

tion

(mg

kg-1

)

0

1

2

3

Treatment

NAT CWG RWR WC WF

N C

once

ntra

tion

(mg

kg-1

)

0

1

2

3

Treatment

NAT CWG RWR WC WF

Treatment

NAT B O WC WF

1995 1995

1997 1997 1997

43

Figure 3.7. Total biomass nitrogen of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russianwildrye, WC - wheat continuous crop, WF - wheat fallow.

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Treatment

NAT CWG RWR WC WF

Tota

l Bio

mas

s N

(g m

-2)

0

10

20

30

40

50

Tota

l Bio

mas

s N

(g m

-2)

0

10

20

30

40

501995 1995 1995

1997 1997 1997


44

(Figure 3.8). In 1997, the same trend was evident in fallow wheat; however, the

magnitude of the difference was smaller. N in the shoot mass of continuous wheat in

1997 was either similar or lower than the other treatments (Figure 3.8). Total N in the

biomass of roots was greater in native grasslands than wheat at all sites and years while

perennial grasses only had lower total root N at the Festuca-Danthonia site in 1997

(Figure 3.9).

Discussion

Cultivating semi-arid and sub-humid native grassland communities and

establishing agronomic cereal and forage monocultures resulted in decreases in R:S and

shifted N distribution from root to shoot mass. The magnitude of the shifts were species-

specific and subject to changes in growing season precipitation and temperature. The

establishment of the agronomic monocultures not only changed plant species

composition but introduced differences in biomass allocation and net primary

productivity. These have significant impacts on ecosystem processes such as soil organic

matter and nutrient dynamics (Tilman and Knops 1997, Hooper and Vitousek 1998,

Craine et al. 2002).

Native communities are useful as benchmarks for measuring changes induced by

anthropogenic disturbances. In these grasslands where moisture availability is variable

and limiting, species diversity, functional differences in N sequestration and partitioning

between species, and niche complementarity may promote long-term stability of the

community type (Tilman et al. 1996, Hooper and Vitousek 1998).

45

Figure 3.8. Total nitrogen in shoot mass of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n = 8). Symbols: B - brome grass, O- orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russianwildrye, WC - wheat continuous crop, WF - wheat fallow.

T rea tm ent

N A T C W G R W R W C W F

T rea tm ent


Tota

l Nitr

ogen

(g m

-2)

0

10

20

30

40

50

Tota

l Nitr

ogen

(g m

-2)

0

10

20

30

40

50

S tipa -B ou te loua S tipa-A gropyron-B oute loua

1995 1995

1997 1997

Festuca-D an thon ia

1995

1997

T rea tm ent

N A T B O W C W FY

Dat

a

46Figure 3.9. Total nitrogen in roots of agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua and

Festuca-Danthonia sites in southern Alberta in 1995 and 1997. Error bars are standard error of the treatment population (n= 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russianwildrye, WC - wheat continuous crop, WF - wheat fallow.

T rea tm ent


T rea tm ent


Tota

l Nitr

ogen

(g m

-2)

0

10

20

30

40

50

Tota

l Nitr

ogen

(g m

-2)

0

10

20

30

40

50

S tipa -B ou te loua S tipa-A gropyron-B oute loua

1995 1995

1997 1997

Festuca-D an thon ia

1995

1997

T rea tm ent

N A T B O W C W F

Y D

ata

47

Native Grassland Communities

Total biomass N in native communities increased in periods of lower growing

season precipitation primarily by increasing root mass which enhances the uptake and

storage of nitrogen (Woodmansee et al. 1978). This leads to N conservation and a

reduction in leaching and volatilization losses from the system (Gleeson and Tilman

1990, Vinton and Burke 1995, Tilman et al. 2002). In Mixed Prairie communities (Stipa-

Bouteloua and Stipa-Agropyron- Bouteloua), increased root mass N with decreased

current growing season precipitation was a result of differences in growth form

(rhizomatous vs. bunchgrass) and rooting depth between the predominant species. During

periods of lower annual growing season precipitation, small bunchgrasses such as

Bouteloua gracilis (Wild. ex Kunth) lag ex Griffiths (blue grama) and Koelaria

macrantha (Ledeb.) J.A. Schultes f. (Junegrass), which have large root: shoot ratios,

allocate the majority of their resources to shallow root systems to more efficiently access

soil moisture near the soil surface, whereas Heterostipa comata (Trin. Rupr.) Barkworth

(needle and thread grass), with deeper roots, accesses deeper sources of soil water and N

(Weaver 1958, Vinton and Burke 1995).

With increased long-term growing season precipitation, Agropyron species

become more prominent in the species mix of native communities. During periods of

above-average current growing season precipitation, the rhizomatous wheatgrasses

(Pascopyrum smithii (Rupr. A. Löve) (western wheatgrass), Elymus albicans (Scrib. and

J.G. Sm.) A. Love (northern wheatgrass), with lower R:S ratios allocate much more N to

shoot mass (Vinton and Burke 1995, Christian 1996) as was evident in reductions in both

48

N concentration and total N in roots and N and N concentration in roots. However, these

species not only lack well developed near-surface water-absorbing systems (Weaver

1958) but lack the ability to reallocate resources from shoots to root systems if current

growing season precipitation is below average.

In the Festuca-Danthonia bunchgrass community, higher long-term annual

growing season rainfall combined with lower evapotranspiration due to lower long-term

growing season temperatures resulted in greater N accumulation in biomass than in

Mixed Prairie systems. During near normal annual growing season precipitation in 1995,

a greater proportion of N accumulated was allocated to shoot mass, while the drier Mixed

Prairie (Stipa-Bouteloua and Stipa-Agropyron-Bouteloua) accumulated more N in root

mass. If the soil water regime of this grassland became drier over the long term, a

corresponding change species composition would be expected.

Annual Monocultures

Annual monocultures such as wheat accumulated less N in biomass than either

introduced perennial monocultures or native communities. The only exception, 1995

fallow wheat at the Stipa-Bouteloua site, was likely due to greater available soil water

and N as a result of later establishment, less cultivation than continuous wheat, and

above-average growing season precipitation.

In annual monocultures, lower biomass N is a result of an inability to store N

above basic requirements for growth. After absorption, this N is assimilated in the leaves

and translocated to the seed head that was removed with the stem at harvest (Murphy and

Lewis 1987, Cramer and Lewis 1993). As current growing season precipitation

49

decreases, the inability of these annuals to reallocate N from leaves to root mass reduces

their ability to further absorb limited water and N, effectively reducing shoot production

(Pate and Farquhar 1988). This reduces harvesting losses but may increase leaching or

volatilization losses. Increased current growing season precipitation increases N

assimilated into shoot mass, which increases losses in N through harvesting. In

ecosystems with less and more variable precipitation, the rate of reduction in biomass N

will be more rapid.

Perennial Monocultures

Perennial monocultures sequestered more N into biomass than annuals but less

than native communities, which was more evident in periods of near normal current

growing season precipitation and is a result of differences in root mass N. However,

lower N concentration in root mass was not evident in the Stipa-Bouteloua site, which

may be the result of the presence of residual roots from the native prairie species due to

the later establishment date for the site. Perennial monocultures did not show a

corresponding increase in shoot mass N except at the Stipa-Bouteloua site in 1995. The

increase at this site was also likely a result of more recent establishment.

Differences in allocation patterns between the species of perennials studied may

modify the rate of reduction in soil N in more moist years. Crested wheatgrass and

smooth brome allocate a greater amount of N to the development of shoot mass than

Russian wildrye and orchardgrass during periods of increased current growing season

precipitation, while the N concentration in shoot mass is higher in the latter species. This

suggests differences in sexual and vegetative reproductive patterns between the species

50

during moist years, which will increase N loss through harvest. The planting and

harvesting of both crested wheatgrass and bromegrass will causing a greater loss of N

from the system than for either Russian wildrye or orchardgrass.

Summary and Conclusions

This research found that annual and perennial agronomic monocultures did not

accumulate more total biomass than native grasslands in the first four years after

plowdown, but there was a decrease in total N in the biomass of these communities

relative to natives. Annual monocultures fixed a greater amount of N into standing crop

than either perennial monocultures or native grasslands and the differences increased

with an increase in current growing season precipitation. In the last year of the study,

perennial monocultures sequestered less total N into biomass than native grassland

communities which may indicate that either these perennial agronomic monocultures

were less efficient at absorbing available mineral N or that the readily available supply

had declined. However, it should be noted that the crowns were not sampled and that the

perennial bunchgrasses (crested wheatgrass and Russian wildrye) were found to have

larger crown masses which serve as an N sink than the native communities. There were

no differences in total shoot mass N between perennial monocultures and native

grasslands in the last year of the study. Standing crop of the perennial monocultures was

larger but the N concentration in the shoot mass was lower, which agrees with work of

other researchers. Total N in the root masses of the perennial grass communities were

not different than native grassland, but the quantity of roots was lower, further agreeing

51

with earlier work.

In the first few years after plow-down, the shift toward aerial partitioning of N at

the expense of root mass is far larger in annual than perennial monocultures. The effect

of continued cultivation, and the inability of the annual species to absorb nutrients above

basic requirements for growth and harvest could continue to reduce the supply of N in the

soil environment. There were changes in partitioning of N in perennial monocultures

with a shift towards more shoot mass; however these changes were much smaller than

expected and do not seem to support the view put forward by Lesica and Deluca (1996).

On the other hand, spring grazing or harvest is the norm for most perennial monocultures

and in this study the monocultures were harvested in the fall. Consequently, the N

content of the standing crop may have been higher in the spring and losses may be

greater than observed in this study. In this study, by the time the standing crop was

harvested, a great deal of the N in the shoot mass may have been translocated to the

crowns and roots (Lawrence 1978).

Although others have suggested that production is higher in these perennial

monocultures over the long-term, this research indicates that immediately after plow-

down, differences in biomass partitioning of N between the perennial monocultures and

native communities are minimal. Continued grazing of these perennial monocultures

during periods of lower growing season precipitation might decrease their productivity

and economic sustainability.

52

References Cited

Burke, I.C., W.K. Lauenroth, and D.G. Milchunas. 1997. Biogeochemistry of managedgrasslands in central North America. In: E.A. Paul, K. Paustian, E.T. Elliott, andC.V. Cole (EDS.). Soil organic matter in temperate agroecosystems. Boca Raton,FL: CRC Press.

Christian, J. 1996. Revegetating abandoned cropland in southwestern Saskatchewanusing native species, alien species and natural succession. M.S. Thesis. Regina,SK: University of Regina. 52 p.

Coupland, R.T. 1961. A reconsideration of grassland classification in the Northern GreatPlains of North America. Journal of Ecology 49:135-167.

Craine C., D. Tilman, D. Wedin, P. Reich, M. Tjoelker, and J. Knops. 2002. Functionaltraits, productivity and effects on N cycling of 33 grassland species. FunctionalEcology 16:563-574.

Cramer, M., and O. Lewis. 1993. The influence of NO3- and NH4

+ nutrition on the gasexchange characteristics of the roots of wheat (Triticum aestivum) and maize (Zeamays) plants. Annals of Botany 72:37-47.

Dormaar, J.F., and W.D. Willms. 1993. Decomposition of blue grama and rough fescueroots in prairie soils.Journal of Range Management 46:207-213.

Dormaar, J.F., M.A. Naeth, W.D. Willms, and D.S. Chanasyk. 1995. Effect of nativeprairie crested wheatgrass (Agropyron cristatum (L.) Gaertn.) and Russianwildrye (Elymus junceus Fisch.) on soil chemical properties. Journal of RangeManagement 49:258-263.

Ellert. B.H., and H.H. Janzen. 1999. Short term influence of tillage on CO2 fluxes from asemiarid soil on the Canadian prairies. Soil and Tillage Research 50:21-32.

Gleeson, S., and D. Tilman.1990. Allocation and the transient dynamics of succession onpoor soils. Ecology 71(3):1144-1155.

Hartnett, D.C., and K.H. Keeler. 1995. Population processes. Chapter 5. In: A. Joern andK.H. Keeler (EDS.). The changing prairie: North American grasslands. Oxford,Great Britain: Oxford University Press. p. 82-99.

Hooper, D., and P. Vitousek. 1998. Effects of plant composition on nutrient cycling.Ecological Monographs 68:121-149.

53

Lawrence, T. 1978. An evaluation of thirty grass populations as forage crops forsouthwestern Saskatchewan. Canadian Journal of Plant Science 58:107-115.

Lesica, P. And T. H. DeLuca. 1996. Long-term harmful effects of crested wheatgrass onGreat Plains grassland Ecosystems. Journal of Soil and Water Conservation51(5):408 -412.

Love, R.A. 1972. Selection and breeding of grasses for forage and other uses. Chapter 5. In: V.B. Younger and C.M. McKell (EDS.). The biology and utilization ofgrasses. New York, NY: Academic Press.

Moss, E.H. 1944. The prairie and associated vegetation of southwestern Alberta.Canadian Journal of Resources 25(C):209-227.

Mueller, I. 1941. An experimental study of rhizomes of certain prairie plants. EcologicalMonographs 11:164-188.

Murphy, A., and O. Lewis. 1987. Effect of nitrogen feeding source on the supply ofnitrogen from root to shoot and the site of nitrogen assimilation in maize (Zea maysL. cv R201). The New Phytologist 107:327-333.

Odum, H.T. 1968. Work circuits and systems stress. In: H.E. Young (ED.) Primaryproductivity and mineral cycling in natural ecosystems. Orono, ME: University ofMaine Press. p. 81-138.

Pate, J.S., and G.D. Farquhar. 1988. Role of the crop plant in cycling of nitrogen. In: J.R.Wilson (ED.). Advances in nitrogen cycling in agricultural systems. WallingfordOxon, United Kingdom: CAB International. p. 23-45.

SAS Institute, Inc. 1999. SAS/STAT user guide. Version 8. Cary, NC: SAS Institute, Inc.3884 p.

Smoliak. S., A. Johnston, and L.E. Lutwick. 1967. Production and durability of crestedwheatgrass in southeastern Alberta. Canadian Journal of Plant Science 47:539-547.

Spedding, C.R.W. 1971. Grassland ecology. Oxford, Great Britain: Oxford University Press.

Steel, R.G.D., and J.H. Torrie. 1980. Principles and procedures of statistics: a biometricalapproach. New York, NY: McGraw Hill Book Co.

Tilman D., D. Wedin, and J. Knops. 1996. Productivity and sustainability influenced bybiodiversity. Nature (London) 379:718-720.

54

Tilman, D., and J. Knops. 1997. The influence of functional diversity on ecosystemprocesses. Science 277:1300-1302.

Tilman, D., J. Knops, D. Wedin, and P. Reich. 2002. Experimental and observationstudies of diversity, productivity and stability: Chapter 3. In: A. Kinzig, S. Pacala,and D. Tilman (EDS.). The functional consequences of biodiversity: empiricalprogress and theoretical extensions. Monographs of Population Biology 33:9-41.

Vinton, M.A., and I.G. Burke. 1995. Interactions between individual plant species andsoil nutrient status in the shortgrass steppe. Ecology 76(4):1116-1133.

Weaver, J.E. 1958. Summary and interpretation of underground development in naturalgrassland communities. Ecological Monographs 28(1):55-78.

Wedin, D.A. 1999. Nitrogen availability: plant:soil feedbacks and grassland stability. In:Eldridge and Freudenberger (EDS.). Sixth International Grassland CongressProceedings. Vol. 1. p. 193-197.

Wedin, D.A., and D. Tilman. 1990. Species effects on nitrogen cycling: a test withperennial grasses. Oecologia 84:433-441.

Whitehead, D.C. 1995. Grassland nitrogen. Wallingford, United Kingdom: CABInternational.

Woodmansee, R., J. Dodd, R. Bowman, F. Clark, and C. Dickinson. 1978. Nitrogenbudget of a shortgrass prairie ecosystem. Oecologia 34: 361-376.

55

CHAPTER 4

SOIL NITROGEN PARTITIONING IN NORTHERN GREAT PLAINSGRASSLANDS: SHORT-TERM RESPONSE TO

AGRONOMIC TREATMENTS

Introduction

Native grassland soils accumulate large pools of nitrogen (N) that are maintained

by microbial replacement of relatively small losses caused by denitrification,

volatilization, leaching, erosion and herbivory, and by rapid recycling of dead biomass

(Rosswell 1976, Stevenson 1982, Bonde and Rosswell 1987). These soils represent a

benchmark that can be used to determine the impacts of cultivation and seeding on the

quantity and quality of soil N.

Soil N is stored in various fractions that differ in stability, availability and rate of

turnover, but only a small labile N fraction is readily available to plants. This labile N

fraction is most sensitive to changes in management or environmental conditions (McGill

et al. 1988). The light fraction (density < 1.7 g cm-3) is part of this dynamic labile fraction

and consists of partially decomposed plant material found near the soil surface. In soils,

the conversion of the light fraction (LF) to available mineral N (NH4+ and NO3

-) occurs

through biochemical transformations mediated by soil microorganisms and is affected by

temperature, moisture and pH (Stevenson 1986, Whitehead 1995). Changes in LF and

mineral N in agronomic systems are influenced by the climate, soil crop and cropping

56

system (Biederbeck et al. 1994, Gregorich et al. 1994, Bayer et al. 2000, Sá et al. 2001,

Diekow et al. 2005). However, these effects are typically reported from studies of

established sites (Stevenson 1986) and do not include changes in soil N partitioning

during the first few years after seeding a native grassland. This research was conducted

at three Northern Great Plains sites, distinguished by varying degrees of aridity, to

determine the soil N response within four years of cultivating native grassland and

seeding with perennial or annual agronomic grasses.


Site Description

The study was conducted at three sites in southern Alberta (Onefour, Lethbridge,

and Stavely) distinguished by plant community, climate, and soil. The Onefour site was

located in southeast Alberta near Manyberries (49o 07' N, 110o 29' W). The Orthic Brown

Chernozemic (Aridic Haploboroll) soils support a Stipa-Bouteloua community with an

average annual precipitation of 332 mm. The Stipa-Agropyron-Bouteloua site near

Lethbridge, in south-central Alberta (49o 43' N, 110o 57'W), has Orthic Dark Brown

Chernozemic (Typic Haploborolls) soils and an annual average precipitation of 402 mm

(Smoliak et al. 1976). The Fescue grassland (Festuca-Danthonia) site was located in the

Porcupine Hills west of Stavely, Alberta (50o 12' N, 113o 57' W). The soils are Orthic

Black Chernozems (Udic Haploborolls), and the average precipitation is 493 mm (Naeth

et al. 1991). Native vegetation of these sites has been described in detail by Moss (1944)

and Coupland (1961).

57

Experimental Design

The effects of cultivation and seeding were tested at each site in a randomized

complete block design with four replicates of five treatments established in 3 x 10 m

plots. The treatments were imposed on previously uncultivated native grassland that

historically had been lightly grazed. During establishment, the research plots were

protected by a fence.

Seeding treatments consisted of two perennial grass monocultures recommended

for each site by Agriculture and Agrifood Canada, and Triticum aestivum L. ‘Katepwa’

(spring wheat) that was either cropped annually or fallowed in alternate years. Native

grassland served as a control. The perennial grasses seeded on the two Mixed Prairie sites

(Stipa-Bouteloua and Stipa-Agropyron-Bouteloua) were Agropyron cristatum (L.) Gaertn

(crested wheatgrass) and Psathystachys juncea (Fisch.) Nevski (Russian wildrye). On the

Fescue prairie site, the seeded perennial grasses were Bromus inermis Leyss. (smooth

bromegrass) and Dactylis glomerata L. (orchardgrass).

The Stipa-Agropyron-Bouteloua and Festuca-Danthonia sites were established in

1993, and the Stipa-Bouteloua site in 1994. The soils were cultivated to an average depth

of 15 cm, and all seeding was done with 15-cm row spacing.

Soil Nitrogen Determination Methods

In the fall of 1995 at all three sites, three 2-cm-diameter soil cores were extracted

from each plot and partitioned into three depth segments: 0 - 7.5 , 7.5 - 15, and 15 - 30

cm. In 1997, one 2-cm core was collected per plot at the same depths. Total N and

mineralizable N were determined for the upper 15 cm, while analysis of the light fraction

58

was completed for the upper 7.5 cm.

Aliquots were obtained from each sample and dried at 105o C for 48 hours to

determine soil water content and bulk density. Stones were removed before oven drying

by screening with 2-mm sieves. The samples were then ground in a rotating sieve (2 mm)

and stored at room temperature until the analyses were completed. Another subsample

was further ground (149 :m) and analysed for C and N using an automated combustion

technique (Carlo ErbaTM, Milan, Italy). Percent soil C and N content were converted to

mass equivalent using bulk density.

Mineralizable N was determined by wetting 50 g oven dried soil to 80% of field

capacity wetness, which was determined using a pressure plate apparatus. These samples

were then incubated at 25o C for eight weeks in airtight 1-L glass jars. Evolved CO2 was

trapped in 10 mL of 2M NaOH. Jars were aerated and NaOH traps replaced at one, four,

and eight weeks. A replacement at two weeks was added in 1997. At the completion of

the incubation, the soils were air-dried and analysed for inorganic N using a Technotron

Autoanalyzer II (Tarrytown, NY). Ammonium was determined according to Industrial

Method No. 98-70W after KCl extraction, while nitrate levels were determined according

to Industrial Method No. 199070W/B (Keeney and Nelson 1982).

The LF was determined using a method utilized by Strickland and Sollins (1987)

and Janzen et al. (1992). A 10-g subsample of coarsely ground soil (2 mm) was dispersed

with sodium iodide (NaI) solution with a specific gravity of 1.70 (± 0.02) using a Vitis

homogeniser (Vitis Co., Gardiner, NY). Suspensions were allowed to settle for 48 hours

at room temperature, and the suspended material was removed using a vacuum and

transferred directly to a Millipore filtration unit (Millipore Corp., Medford, MA) with

59

Whatman No. 1 filter. The soil was suspended a second time to ensure complete

recovery. The light fraction was washed, oven-dried (60oC), weighed, ground using a 149

Fm mesh, and analysed for C and N using an automated dry weight combustion

technique (Carlo ErbaTM, Milan, Italy). Due to difference in light fraction sample

preparation between years, 1995 native grassland values were used as a reference to

adjust 1997 results.

Statistical Analyses

Each variable was analysed in a whole model as an unbalanced 3 (sites) x 3

(treatments) x 2 (years) x 4 (replicates) split-split plot design using the GLM Procedure

of SAS (1999). The potential bias resulting from repeated measurements over years was

alleviated using the Box Correction Procedure (Milliken and Johnson 1984). The analysis

was unbalanced because the perennial grass species were pooled, as were the wheat

cropping systems, resulting in twice the number of observations that were present in the

native treatments. The variables were highly responsive to the factors tested, and due to

interactions meaningful interpretation required a more detailed examination of the data.

This was accomplished by analysing the data within sites, and the grass species as

individual treatments, as a 5 (treatments) x 2 (years) x 4 (replicates) split plot design.

Means separation was achieved using single degree of freedom contrasts (Steel and

Torrie 1980). Those contrasts are found in the appendices. Significant difference

between treatment means was evaluated at P < 0.05.

60

Results

Precipitation during the 1995 growing season (March to September) at all three

sites decreased as Stipa-Bouteloua > Stipa-Agropyron-Bouteloua > Festuca-Danthonia

(Table 4.1). In 1996, precipitation at the Festuca-Danthonia and Stipa-Agropyron-

Bouteloua sites was well below the long-term average, but near average at the Stipa-

Bouteloua site (Table 4.1). In 1997, all three sites experienced near average growing

season precipitation (Table 4.1).

The treatment effect on most variables examined in this study was affected by

site, year of sampling, and their interactions (Table 4.2). The soil light fraction, light

fraction N, and the concentrations of soil N and NO3- followed a trend of Stipa-Bouteloua

< Stipa-Agropyron-Bouteloua < Festuca-Danthonia, while the concentrations of

mineralizable N and NH4+ were smallest for the Stipa-Agropyron-Bouteloua site. Site had

little impact on the treatment response of pooled perennial grass and wheat treatments

(Table 4.2). The light fraction of wheat declined between 30 and 38% compared to native

grasslands by 1995 and further declined to 60 to 73% of native values by 1997, except at

the Stipa-Bouteloua site in 1995 (Figure 4.1). The lack of treatment effect at this site was

probably a result of its later establishment date. The light fraction of the perennial grass

treatments was 38 and 50% of native grasslands in 1995 but rebounded to between 50 to

65% of native grasslands in 1997 (Figure 4.1). The drop in the light fraction of wheat and

perennial grasses resulted in a corresponding drop in light fraction N; however, there

were few significant differences between any of the perennial species utilized at any of

the three sites (Figure 4.2).

61

Table 4.1. Monthly precipitation (mm) over the growing season from 1995 to 1997 atthree sites in southern Alberta.


Stipa-Bouteloua

1995 17 37 41 130 56 50 48 379 148

1996 32 13 64 80 33 4 51 277 109

1997 28 15 84 65 11 23 20 246 96

Ave. 2 22 28 41 64 34 39 27 255 100


1995 10 38 106 138 66 44 19 421 137

1996 21 22 54 18 5 70 6 196 64

1997 33 14 96 101 32 33 10 319 104

Ave. 2 24 31 55 74 42 42 40 308 100

Festuca-Danthonia 3

1995 6 23 72 84 69 39 63 356 83

1996 45 24 72 49 7 4 54 255 60

1997 15 21 138 73 28 77 35 387 91

Ave.3 24 14 99 113 74 69 34 427 100

1 Percent of 50-year average.2 50-year averages - Agriculture and Agrifood Canada.3 Measured at Claresholm.

At the Stipa-Bouteloua site, cultivating and seeding of agronomic species

reduced mineralizable soil N in 1997 but not in 1995 (Figure 4.3). At the Stipa-

Agropyron-Bouteloua site, mineralizable N increased by cultivating and seeding in 1995,

but by 1997 the effect was evident only in wheat treatments (Figure 4.3) while at the

Festuca-Danthonia site, mineralizable N was not affected (Figure 4.3).

62

Table 4.2. Total model for total soil nitrogen, mineralizable nitrogen, C:N in soil,ammonium (NH4

+), nitrate (NO3-), light fraction (LF), and total light fraction

nitrogen at three southern Alberta sites in 1995 and 1997.

Mineralizable N (mg kg-1) NH4+ (mg kg-1) NO3

- (mg kg-1) LF (mg g-1) Total LF N (mg kg-1)

Source ----------------------------------------------------------------------Probabilities---------------------------------------------------------------------

Year (Y) 0.006 <0.001 0.360 <0.001 <0.001

Site (S) <0.001 <0.001 0.013 <0.001 <0.001

Treatment (T) 0.163 0.318 <0.001 <0.001 <0.001

S x Y 0.012 <0.001 0.005 <0.001 <0.001

T x Y 0.248 0.468 <0.001 <0.001 <0.001

T x S 0.674 0.513 0.282 <0.049 <0.031

S x Y x T 0.891 0.505 0.041 <0.001 <0.001

Site ---------------------------------------------------------------------------Means------------------------------------------------------------------------

Stipa-Bouteloua

Native 52.580 8.400 1.990 26.340 345.000

Perennial Grass1 41.300 7.700 2.500 15.850 205.000

Wheat2 40.980 8.270 5.500 12.780 172.000

SE 9.680 2.040 0.900 6.740 140.000


Native 31.950 7.030 2.650 40.620 670.000

Perennial Grass1 27.260 6.690 2.390 21.100 310.000

Wheat2 35.730 6.800 6.650 15.390 240.000

SE 9.680 2.040 0.900 6.740 140.000

Festuca-Danthonia

Native 149.420 17.030 2.860 74.790 1410.000

Perennial Grass1 131.390 16.390 4.240 40.070 690.000

Wheat2 147.100 20.620 9.220 25.680 430.000

SE 9.680 2.040 0.900 5.830 140.000

1 Results a combination of crested wheatgrass and Russian wildrye.2 Results a combination of fallow and continuously cropped wheat. 3 Results a combination of smooth bromegrass and orchardgrass.

Treatment

NAT B O WC WF

1997


Ligh

t Fra

ctio

n (g

kg-1

)

0

20

40

60

80

100

120

140

160

Treatment

NAT CWG RWR WC WF

Ligh

t Fra

ctio

n (g

kg-1

)

0

20

40

60

80

100

120

140

160

Treatment

NAT CWG RWR WC WF

1995 1995 1995

1997 1997

63

Figure 4.1. Light fraction (LF) concentrations in the upper 7.5 cm of agronomic and native communities in Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in 1995 and 1997. Error bars are the standard error of treatment means (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russian wildrye, WC - wheat continuous crop, WF - wheat fallow.

64

Figure 4.2. Total nitrogen content of the light fraction (LFN) in the upper 7.5 cm of the soil under agronomic and nativecommunities at Stipa-Bouteloua (SB), Stipa-Agropyron-Bouteloua (SAB), and Festuca-Danthonia (FD) sites in 1995and 1997. Error bars are the standard error of treatment means (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russian wildrye, WC - wheat continuous crop, WF - wheatfallow.

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Treatment

NAT CWG RWR WC WF

Ligh

t Fra

ctio

n N

(mg

kg-1)

0

500

1000

1500

2000

2500

3000

Ligh

t Fra

ctio

n N

(mg

kg-1)

0

500

1000

1500

2000

2500

30001995

1997

1995

1997

1995

1997


65

Figure 4.3. Mineralizable N in the upper 15 cm of the soil under agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in 1995 and 1997. Error bars are the standard error of treatment (n =8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - native grassland, RWR - Russian wildrye, WC - wheat continuous crop, WF - wheat fallow.

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Treatment

NAT CWG RWR WC WF

Min

eral

izab

le N

(mg

kg -1

)

0

50

100

150

200

250

Min

eral

izab

le N

(mg

kg -1

)

0

50

100

150

200

250

Stipa-Bouteloua

1995

1997

1995

1997

1995

1997

Stipa-Agropyron-Bouteloua Festuca-Danthonia

66

At the Stipa-Bouteloua and Stipa-Agropyron Bouteloua sites, wheat treatments

resulted in greater soil NO3- concentrations than either perennial or native grass

communities in both years (Figure 4.4). In 1995, the results were similar at the Festuca-

Danthonia site but in 1997 NO3 - concentration in wheat was higher than the native

grasslands but not different from perennial grasses (Figure 4.4).

Discussion

Cultivation and seeding had no effect on total N in the first 15 cm soil depth, but

it did influence the light fraction found in the upper 7.5 cm at all sites. Site treatment

responses were different only for the variables derived from the light fraction. However,

magnitudes were different rather than ranking. A greater reduction in light fraction and

light fraction N at the Stipa-Bouteloua site than at Stipa-Agropyron-Bouteloua or

Festuca-Danthonia sites was expected, since the labile pool of nitrogen at this site is

more prone to thermal and physical decomposition through freeze-thaw and wet-dry

cycles than at the other sites (Dormaar 1975, Lutwick and Dormaar 1976). However,

physical changes in the soil environment caused by cultivation may have reduced thermal

and moisture variability in the soil resulting in reduced decomposition or the pool was

less dynamic.

Cultivation and seeding of native grasslands may modify soil N partitions through

the mixing of the soil, incorporation of vegetation, changes in the soil temperature and

moisture regimes, and changing microorganism activity. The direct effect of mixing on

total soil N was negligible, since the plow layer imposed during cultivation was shallower

67

Figure 4.4. Nitrate content in the upper 15 cm of the soil under agronomic and native communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in 1995 and 1997. Error bars are the standard error of treatment means (n = 8). Symbols: B - brome grass, O - orchardgrass, CWG - crested wheatgrass, NAT - nativegrassland, RWR -Russian wildrye, WC - wheat continuous crop, WF - wheat fallow.

Treatment

NAT CWG RWR WC WF

1997

Treatment

NAT B O WC WF

Treatment

NAT CWG RWR WC WF

Nitr

ate

(mg

kg -1

)

0

2

4

6

8

10

12

14

161997

1995

Nitr

ate

(mg

kg -1

)

0

2

4

6

8

10

12

14

161995 1995

1997


68

than the Ah horizons at all three sites; however, it may partially explain the reduction in

light fraction and light fraction N in the upper 7.5 cm of the soil because cultivation

exceeded that depth. At these sites, 73 to 91% of the N contained in these native

communities is partitioned into root mass. Cultivation caused the death of this root mass,

which may have modified the quantity and quality of the light fraction.

Cultivation disturbs soil structure and macerates roots which increases microsite

availability for microorganism activity and alters soil microbial communities due to

changes in soil temperature and moisture regimes. (Rovira and Graecen 1957, Kennedy

1999, Calderón et al. 2001). These modifications may have increased mineralization of

the light fraction, reduced light fraction N and increased soil nitrate (NO3-) concentrations

(Entz et al. 2001, Calderón and Jackson 2002).

The increased soil nitrate concentations created by cultivation may be lost from

the system in a variety of ways. Since agronomic species have been modified to

maximize shoot production, a proportion of the absorbed nitrate is assimilated into shoot

biomass, most of which is removed through harvest (McGill et al. 1981). Secondly, since

nitrate is soluble in water as precipitation increases in amount or intensity, losses may

occur through erosion or leaching (Davidson et al. 1990, Bayer et al. 2000, Malhi et al.

2002). Tillage method, timing and frequency of tillage also increase erosion or leaching

losses (Ritter et al. 2005). Lastly, denitrificaton and volatilization causes losses of soil

nitrate from agronomic systems. Increased levels N20 can be attibuted to higher soil

moisture and temperature created by cultivation (Horgan et al. 2002) and losses may

occur from bare soil or through the transpiration stream (Chang et al. 1998, Smart and

69

Bloom 2001). The amount of nitrate in the soil profile can be reduced with no-till and

continuous cropping systems that include perennial plants (Weed and Anwar 1997, Entz

et al. 2001).

Light fraction and light fraction N in the soil of all treatments were generally

lower at the Stipa-Bouteloua site than at the Stipa-Agropyron-Bouteloua and Festuca-

Danthonia sites. This suggests a positive correlation between the quantity of light

fraction and long- term growing season precipitation levels. By 1997, the light fraction

under wheat had declined 73% at the Festuca Danthonia site and 60% the Stipa-

Bouteloua site. With mean growing season precipitation less limiting at the Festuca-

Danthonia site, changes in soil temperature caused by cultivation, removal of the plant

canopy, aggregate disruption and changes in root input may have allowed greater

mineralization of the light fraction. At the drier Stipa-Bouteloua site, however, water may

have been the primary factor limiting microbial populations and mineralization of the

light fraction.

The rate of reduction in the light fraction and light fraction N components

increased with cultivation and planting of annual species. When planting perennial

species, there were no significant losses in light fraction or light fraction N over the

short-term; however, continued harvest may cause reductions in both.


Four years after converting native prairie grass into agronomic crops, there was

no change in total N, mineralizable N or ammonium in perennial and annual crop species,

70

but there were large changes in the LF and LFN.

The absence of short-term changes in total soil N was expected due to the large

size of the pool in grassland soils. However the lack of difference in mineralizeable N

does not agree with work done in Wyoming that found native grasslands had higher

mineralizable N than selected agronomic treatments. The typical increases in soil

temperature, moisture and oxygen due to cultivation led to increased mineralization. In

the first four years there was a marked increase in nitrate in annual monocultures,

indicating that the rate of mineralization was elevated immediately after plow-down and

cultivation of the native grasslands. This agrees with other studies that found increased

mineralization with cultivation and nitrate concentration which was attributed to

breakdown and mineralization of soil organic matter.

In contrast to patterns recorded under agronomic crops, there were no differences

in nitrate content between native grasslands and perennial monocultures. This response

does not agree with work done on different perennial grass species which were found

have up to tenfold differences in annual net mineralization after only three years, and

which were attributed to differences in nitrogen concentrations in below ground biomass.

However, there were few differences in the nitrate concentration of root tissue between

crested wheatgrass, Russian wildrye and native communities in this study. The lack of

difference in nitrate concentrations could have been due to the short period of time since

plow-down and the effect of the decomposing relic root masses of the native species.

In the last year of the study, light fraction N was lowest in annual monocultures

which agrees with other work done in Canada. Low LFN was thought to be due to a

71

combination of tillage effects and reductions in root mass following plowdown. In this

study perennial agronomic monocultures had a higher LFN than the annual monocultures

and lower than native grasslands with few differences between the various perennial

species. The intermediate position occupied by the perennial monocultures was likely a

result of the single tillage event rather than differences in species root mass.

With adequate moisture and proper management these monocultures will likely

continue to produce greater above ground biomass for a period of time. However it will

be at the expense of N reserves in the soil. At some point, lower N available for growth

will likely limit the amount of useable forage and the economic benefits of maintaining

these monocultures. At that time the accumulated changes to ecological processes and

diversify may limit our ability to reestablish native multi-species communities

72

References Cited

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Biederbeck, V.O., H.H. Janzen, C.A. Campbell, and R.L. Zentner. 1994. Labile soilorganic matter as influenced by cropping practices in an arid environment. SoilBiology and Biochemistry 26(12):1647-1656.

Bonde, T.A., and T. Rosswell. 1987. Seasonal variations of potentially mineralizablenitrogen in four cropping systems. Soil Science Society of America Journal 51:1508-1514.

Calderón, F.J. and L.E. Jackson. 2002. Rototillage, disking and subsequent airrigation:

Effects on soil nitrogen dynamics, microbial biomass and carbon dioxide efflux.Journal of Environmental Quality. 31: 752-758.

Calderón, F.J., L.E. Jackson, K.M. Scow, and D.E. Rolston. 2001. Short-term dynamicsof nitrogen, microbial activity and phospholipid fatty acids after tillage. SoilSociety of American Journal 65:118-126.

Chang,C., H.H. Janzen, C.M. Cho, and E.M. Nakonechny. 1998. Soil Science Society ofAmerican Journal. 62(1): 35-38.

Coupland, R.T. 1961. A reconsideration of grassland classification in the northern greatplains of North America. Journal of Ecology 49:135-167.

Davidson, E.A., J.M. Stark, and M.K. Firestone. 1990. Microbial production andconsumption of nitrate in annual grasslands. Ecology 71:1968-1975.

Diekow, J., Mielniczuk, J., Knicker, H., Bayer, C., Dick, D., and I. Kogel-Knabner. 2005.Carbon and nitrogen stocks in physical fractions of a subtropical Aerisol asinfluenced by long-term no till cropping systems and N fertilization. Plant andSoil 268: 319-328.

Dormaar, J.F. 1975. Susceptibility of organic matter of chernozemic Ah horizons tobiological decomposition. Canadian Journal of Soil Science 55:473-480.

Entz, M.H. Bullied, W.J., Forster, D.A. Gulden, R. And J.K. Vessey. 2001. Extractrion ofSubsoil N by Alfalfa, Alfaalfa-Wheat, and perennial grass systems. AgronomyJournal 93:495-503.

73

Gregorich, E.G., M.R. Carter, D.A. Angers, C.M. Montreal, and B.H. Ellert. 1994.Towards a minimum data set to assess soil organic quality. Canadian Journal ofSoil Science 74:367-385.

Horgan, B.P., B.E. Brandon, and R.L. Mulvaney. 2002. Direct measurement ofdenitrification using 15N labelled fertiliaer applied to turfgrass. Crop Science 1602 - 1610.

Janzen, H.H., C.A. Campbell, S.A. Brandt, G.P. Lafond, and L. Townley Smith. 1992. Light fraction organic matter in soils from long-term crop rotations. Soil Scienceof American Journal 56:1799-1806.

Keeney, D. R., and D. W. Nelson. 1982. In A.L. Page (Ed.) Methods of Soil AnalysisPart 2. American Society of Agronomy. Madison WI, p. 648-693.

Kennedy, A.C. 1999. Microbial diversity in agroecosystem quality, p. 1-17. In: W.W. Collins and C.O. Qualset (Eds.). Biodiversity in agroecosystems. New York: CRCPress.

Lutwick, L.E., and J.F. Dormaar. 1976. Relationships between the nature of soil organic matter and root lignins of grasses in a zonal sequence of Chernozemic soils.Canadian Journal of Soil Science 56:363-371.

Malhi, S.S., S.A. Brandt, D. Ulrich, R. Lemke, and K.S. Gill. 2002. Accumulation andDisturbution of Nitrate-Nitrogen and Extractable Phosporus in the soil profoleunder various croppping systems. Journal of Plant Nutrition 25(11): 2499-2520.

McGill, W.B., C.A. Campbell, J.F. Dormaar, E.A. Paul, and D.W. Anderson. 1981. Soil organic matter losses. Proc. 18th Annual Soil Science Workshop. Edmonton, AB.133 p.

McGill, W.B., J.F. Dormaar, and E. Reinl-Dwyer. 1988. New perspectives on soilorganic matter, quality, quantity and dynamics on the Canadian Prairies. In: Land degradation and conservation tillage. Proc. Annual Canadian Soil ScienceMeeting. Calgary, AB. p. 30-48.

Milliken, G.A., D.E. Johnson. 1984. Analysis of messy data, Volume 1: Designedexperiments. Van Nostrand Reinhold. New York, NY. 473p.

Moss, E.H. 1944. The prairie and associated vegetation of southwestern Alberta. Canadian Journal of Resources 25(C):209-227.

Naeth, M.A., A.W. Bailey, D.S. Chanasyk, and D.J. Pluth. 1991. Water holding capacity

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of litter and soil organic matter in Mixed Prairie and Fescue grassland ecosystemsof Alberta. Journal of Range Management 44(1):13-17.

Ritter, E., M. Starr, and L. Vesterdal. 2005. Losses of nitrate from gaps of different sizesin a managed beech (Fagus sylvatica) forest. Canadian Journal of ForestryResearch. 35: 308-319.

Rosswell, T. 1976. The internal cycle between microorganisms, vegetation and soil. In: B.H. Stevenson and R. Soderlund (Eds.). Nitrogen, phosphorous and sulphur - global cycles. Stockholm, Sweden: Ecological Bulletin. p. 157-167.

Rovira, A.D., and E.L. Graecen. 1957. The effect of aggregate disruption on the activitiesof microorganisms in the soil. Australian Journal of Agricultural Research 8:659-673.

Sá, J.C., Cerri, Dick, W.A., Lal, R., Venko-Filho, S.P., Piccolo, M.C., and B.E. Feigl. 2001. Organic matter dynamics and carbon sequestraton rates for a tillagechronosequence in a Brazilian Oxisol. Soil Science Society of America Journal65: 1486-1499.

SAS Institute, Inc. 1999. SAS/STAT user guide. Version 8. Cary, NC: SAS Institute Inc. 3884 p.

Smart, D.R. and A.J. Bloom. 2001. Wheat leaves emit nitrous oxide during nitrateassimilations. Proceedings of the National Academy of Sciences. 98(14): 7875 -7878.

Smoliak, S., A. Johnston, M.R. Kilcher, and R.W. Lodge. 1976. Management of prairierangeland. Publication 1425. Ottawa, ON: Information Division, Department ofAgriculture. 30 p.

Steel, R.G.T., and J.H. Torrie. 1980. Principles and procedures of statistics: a biometrical approach. New York, NY: McGraw Hill Book Co.

Stevenson, F.J. 1982. Origin and distribution of nitrogen in soil, p 1-39. In: F.J. Stevenson (ED.). Nitrogen in agricultural soils. New York, NY: Academic Press.

Stevenson, F.J. 1986. Cycles of soils: C, N, P, S, and micronutrients. New York, NY: Wiley Interscience.

75

Strickland, T.C., and P. Sollins. 1987. Improved method for separating light and heavy fraction organic material from soil. Soil Science Society of America Journal 51:1390-1393.

Weed, D.A.J., and Anwar. 1997. Nitrate and water present in and flowig from root zonesoil. Journal of environmental Quality. 25:709-719.

Whitehead, D.C. 1995. Grassland nitrogen, 397 p. Wallingford. UK: CAB International.

76

CHAPTER 5

WATER UPTAKE RESUMPTION FOLLOWING SOIL DROUGHT:A COMPARISON BETWEEN NATIVE AND

AGRONOMIC COMMUNITIES

Introduction

In an environment with low, variable growing season precipitation, high

evapotranspiration and frequent droughts, the Stipa-Bouteloua (needle and thread grass -

blue grama grass) community of the Northern Great Plains of southeastern Alberta,

Canada has evolved a stable assemblage of functionally diverse species that occupy

complementary niches (Tilman et al. 1996, Hooper and Vitousek 1998). In both dominant

species found in this dry mixed grass community {Heterostipa comata (Trin. Rupr.)

Barkworth (needle and thread grass) and Bouteloua gracilis (Wild ex Kunth) lag ex

Griffiths (blue grama grass), a large proportion of assimilated resources are allocated to

root mass to better use limited soil water. Needle and thread grass, a C3 species, has a

broad, deep, well-branched rooting system which effectively uses deeper early-season

soil water, whereas the shallow rooted C4 blue grama grass has a high capacity for fine

root proliferation and rapid water uptake after convection storms later in the growing

season (Smoliak 1956, Weaver 1958, Coupland and Johnson 1965, Sala and Lauenroth

1982, Hook and Lauenroth 1994).

77

Over the last 60 years, millions of hectares of this grassland have been cultivated

and replaced by monocultures of Agropyron cristatum (L.) Gaertn. (crested wheatgrass)

and Psathyrostachs juncea (Fisch.) Nevski (Russian wildrye) (Dormaar 1978, Christian

and Wilson 1999). Both of these C3 bunchgrasses have widespread and deep root systems

that efficiently access limited soil water supplies (Smoliak and Johnston 1980). In

addition, crested wheatgrass roots have been shown to lift absorbed water from deeper

parts of the soil profile and release it into shallower layers (Caldwell et al. 1998). This

hydraulic lift not only maintains shallower roots but enhances soil biochemical

conditions, nutrient availability and acquisition by roots. These characteristics may result

in the creation of a competitive advantage over native communities (Bittman and

Simpson 1989, Caldwell et al. 1998). The potential for hydraulic lift in Russian wildrye

and the dry mixed prairie has not been reported.

In both cultivated and uncultivated semiarid grasslands, temporal and spatial

differences in water availability combined with heterogeneity of soil resources are

important factors in determining the structure and dynamics of plant communities. An

understanding of species and community differences in soil-water-root relationships will

enhance our ability to effectively manage plant, soil, and water resources, allow the

design of multi-crop agro-ecosystems that more fully exploit below-ground niches, and

increase our understanding of invasive plant infestation and management (Noy-Meir

1973, Frank and Bauer 1991, Grime 1994, Sheley and Larson 1995, Wraith and Wright

1998).

78

Drought is a common characteristic of the semi-arid environments in which these

species have evolved. During drought periods, short duration high intensity convection

storms may occur in the summer. The objective of this study was to compare the rate of

water uptake of needle and thread - blue grama grass, crested wheatgrass, and Russian

wildrye communities after simulated drought periods. The information from this research

may provide a greater understanding of functional characteristics which allow long-term

survival of introduced grass monocultures after plowdown and seeding of native

grasslands.


Description of Source Material Sites

The needle and thread grass - blue grama grassland community at the Onefour

substation of Agriculture and Agri-Food Canada near Manyberries, Alberta, Canada (49o

07' N, 110o 29' W) has a long-term annual average precipitation of 332 mm, with 247 mm

or 74.3% falling during the March-through-September growing season. During that

period, 54% (133 mm) falls from April to June, and 27% (66 mm) in July and August

(Agriculture and Agri-food Canada). The vegetation of this community has been

described in detail by Moss (1944) and Coupland (1961).

Experimental Design

In 1994, crested wheatgrass and Russian wildrye communities were established in

3 m x 10 m plots at Onefour on previously uncultivated native grassland that had a

history of light grazing. At the time of establishment, the sites were protected by a fence.

79

In July 1997, five 38-cm diameter, 15-cm deep sods were obtained from each of

the three field treatments: crested wheatgrass, Russian wildrye, and native (needle and

thread - blue grama grass) communities. These sods were transported to a controlled-

environment greenhouse at Montana State University (Bozeman, Montana, USA) where

each was transplanted into a 250-L barrel filled with sandy loam soil. Each barrel was

packed in 15-cm increments to a bulk density of 1.26 g cm- 3. Time domain reflectometry

(TDR) probes (30-cm length) (Topp et al. 1980) were placed horizontally at 7.5, 15, and

60 cm depths within each barrel. Each probe was attached to a series of coaxial

multiplexers (SDMX50, Campbell Scientific. Inc., Logan, UT, USA). A Tektronix

1502C (Beaverton, OR, USA) metallic TDR cable tester controlled by a 21X datalogger

(Campbell Scientific, Inc.) allowed for hourly recording of volumetric water content (2)

for the three depths in each column.

Supplemental illumination by 1000 W metal halide lamps created 14-h

daylengths, with 1-h ramp periods in the morning and evening. Air temperatures

fluctuated between 15o C (night) and 20-25o C (day) with an uncontrolled RH of 0.2 to

0.4 (HMP35C, Vaisala. Inc., Woburn, MA, USA) over the period of the study.

The planted columns were allowed to establish for 11 months until the first week

of June 1998, at which time watering ceased. On July 29, when soil water content of the

column at all depths stabilized near -1.5 MPa matric potential equivalent as determined

via a pressure plate apparatus, water was added to each column to bring the soil in the

column to 0.01 MPa wetness to a 30 cm depth. Soil water content was monitored at each

depth hourly for six 7-d periods between calendar day 210 and 295 of 1998. The first

80

Figure 5.1. Changes in soil water content during six rewetting sequences betweenCalendar Day 210 and 245 of 1998, at 7.5, 15, and 30 cm soil depths incrested wheatgrass, Russian wildrye, and needle and thread - blue gramagrass communities grown in columns at the controlled-environmentgreenhouse at Montana State University, Bozeman, MT. Re-wet sequences 1 to 6 progress in order from left to right in each of the graphs

Soi

l Wat

er C

onte

nt (m

3 m-3

soil)

0 .0 5

0 .1 0

0 .1 5

0 .2 0

0 .2 5

0 .3 0

0 .3 5

0 .4 0

D a y o f 1 9 9 8

2 0 0 2 2 0 2 4 0 2 6 0 2 8 0 3 0 0

Soi

l Wat

er C

onte

nt (m

3 m-3

soi

l)

0 .0 6

0 .0 8

0 .1 0

0 .1 2

0 .1 4

0 .1 6

0 .1 8

C re s te d w h e a tg ra s sR u ss ia n w ild ryeN e e d le -a n d -th re a d - b lu e g ra m a g ra ss

D e p th 3 0 c m

Soi

l Wat

er C

onte

nt (m

3 m-3

soi

l)

0 .0 5

0 .1 0

0 .1 5

0 .2 0

0 .2 5

0 .3 0

0 .3 5

D e p th 7 .5 cm

D e p th 1 5 cm

81

re-wet occurred on day 210, the second on day 217, the third on 244, the fourth on 251,

the fifth on 273 and the sixth on 280 (Figure 5.1). On each re-wet, an amount of water

was added to each column to bring them back to 0.01 MPa matric potential equivalent.

For each 7-d period, the slope of the 2 time series was determined by linear regression

(R2>0.85) for 7.5 and 15 cm depths in each column. The rate of soil water uptake

(mm h-1) was also determined for each 7-d period by multiplying the change in 2 by the

estimated depth of the horizontal TDR probe measurement sensitivity (4 cm). Since

relative humidity and wind speed were fairly uniform in the greenhouse, spatial

differences in evaporation were not considered significant for the randomly located

treatment columns.

The soil water data were analyzed separately for the initial (1, 3, and 5) and

second (2, 4, and 6) re-wets using the MIXED procedure from SAS (SAS Institute, Inc.

2005). Community, time, and their interaction were considered in the model as fixed

effects. Re-wet sequences were treated as repeated measures and different variance-

covariance structures were fitted; the one with the lowest AIC value was selected for the

final analysis. The UNIVARIATE procedure was used to test the residuals for normality

and for obvious outliers. Differences among slope means were evaluated for significance

using an LSD test (SAS Institute, Inc. 2005) with significance determined at LSD < 0.05.

Results

Although there appeared to be a greater rate of water uptake at 7.5 cm in the

needle and thread-blue grama grass community (Figure 5.2 and 5.3), there were no

82

Figure 5.2. Mean changes in soil water content during the first two re-wetting sequences(re-wet 1 and 2) between Day 210 and 245 of 1998 at 7.5 and 15 cm soildepths in crested wheatgrass, Russian wildrye, and needle and thread - bluegrama grass communities grown in columns at the controlled-environmentgreenhouse at Montana State University, Bozeman, MT.

Soil

Wat

er C

onte

nt (m

3 m-3

soi

l)

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Day of 1998

205 210 215 220 225 230 235 240 245

Soi

l Wat

er C

onte

nt (m

3 m-3

of s

oil)

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Crested wheatgrassRussian wildryeNeedle-and-thread - blue grama grass

7.5 cm depth

15 cm depth

83

Figure 5.3. Mean changes in soil water content during the second two re-wettingsequences (re-wet 3 and 4) between Day 245 and 275 of 1998 at 7.5 and 15cm soil depths in crested wheatgrass, Russian wildrye, and needle and thread- blue grama grass communities grown in columns at the controlled-environment greenhouse at Montana State University, Bozeman, MT.

Soi

l Wat

er C

onte

nt (m

3 m-3

)

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Day of 1998

240 245 250 255 260 265 270 275

Soi

l Wat

er C

onte

nt (m

3 m-3

soi

l)

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Crested wheatgrasRussian wildryeNeedle and thread- blue grams grass

15 cm depth

7.5 cm depth

84

significant differences between water uptake rates at 7.5 and 15 cm depths within or

between communities following any of the re-wetting periods. There was a

significant difference between all re-wet sequences, with slopes for re-wets 2 and 3

steeper (more negative) than for re-wet sequences 1, 4, 5 and 6 for all three grass

communities (Table 5.1). The rate of water uptake at 15 cm was approximately three

times the rate at 7.5 cm after the first pulse of water but following subsequent pulses the

rates at 15 cm were either equal to or lower than for 7.5 cm depth (Table 5.2).

Discussion

Water Uptake Following Periods of Drought

Surface soils dry more rapidly and to a greater extent than do deeper layers during

prolonged drought as a result of direct soil evaporation combined with high root density

(Sala et al. 1992, Soon 1988). Grasses concentrate their roots in the upper part of the soil

profile (Weaver 1958, Sims et al. 1978) and as expected there was reduced water uptake

rate for the first re-wet for all three communities when compared with the subsequent re-

wet sequences that followed shorter periods between water addition. This agrees with

previous work that included different species, plant forms and stages of development

(Wraith and Baker 1991, BassiriRad and Caldwell 1992, Wraith et al. 1995). Sala et al.

(1982) suggested that the extent of this after-effect of drought may depend on the

duration and magnitude of the drought.

A lower rate of water absorption immediately after a dry-down period than would

be observed during well-watered periods may be caused by a variety of factors including

85

Table 5.1. Linear regression slope of change in soil water content, and P values for the probability of differences in slope withineach re-wet for six 7-day re-wet sequences from Day 210 to 295 of 1998 in crested wheatgrass, Russian wildrye, andneedle and thread - blue grama grass communities planted in columns in a controlled-environment greenhouse atMontana State University, Bozeman, MT.

Slopes of Re-wet Sequences (SE)1

Treatment Slope 1 Slope 2 Slope 3 Slope 4 Slope 5 Slope 6

Crested Wheatgrass(CWG)

-0.0085 (0.0008)

-0.0126 (0.0012)

-0.0149 (0.0011)

-0.0119 (0.0013)

- 0.0107 (0.0010)

-0.0106(0.0011)

Russian Wildrye(RWR)

-0.0081 (0.0010)

-0.0127 (0.0011)

-0.0157 (0.0009)

-0.0114 (0.0014)

-0.0106 (0.0014)

-0.0106(0.0013)

Needle and Thread -Blue Grama Grass(Native)

-0.0099 (0.0006)

-0.0150 (0.0011)

-0.0171 (0.0011)

-0.0140 (0.0012)

-0.0105 (0.0005)

-0.0106(0.0013)

Contrast -----------------------------------------------------------------------Probability of Differences in Slope-----------------------------------

CWG vs RWR 0.686 0.943 0.567 0.329 0.786 0.981

Native vs CWG 0.314 0.147 0.129 0.180 0.855 0.719

Native vs RWR 0.158 0.167 0.337 0.030 0.925 0.701

1 - the numbers in brackets are the standard errors of the mean

86

Table 5.2. Water uptake rates (mm h-1) for six 7-day re-wet sequences from Day 210 to295 of 1998 in crested wheatgrass, Russian wildrye, and needle and thread -blue grama grass communities planted in columns in a controlled-environment greenhouse at Montana State University, Bozeman, MT.

Treatment TreatmentCWG RWR NAT CWG RWR NAT

Depth Re-wet Water uptake Rate (mm h-1) Re-wet Water uptake Rate (mm h-1)

7.5 1 0.004 0.004 0.004 2 0.025 0.025 0.03015 1 0.014 0.012 0.012 2 0.018 0.020 0.023

7.5 3 0.026 0.028 0.031 4 0.026 0.013 0.02115 3 0.023 0.024 0.020 4 0.015 0.010 0.023

7.5 5 0.022 0.023 0.020 6 0.022 0.022 0.02115 5 0.015 0.017 0.017 6 0.016 0.015 0.0016

root death, xylem embolism, cortical lacunae, increasing suberization and cell wall

adjustment (Ares 1975, North and Nobel 1991, Neumann 1995), while the subsequent

increase in the rate of water uptake after a period of time may be the result of renewed

permeability or function of existing roots, growth of new un-suberized roots or a

combination of both (BassiriRad and Caldwell 1992, Huang and Nobel 1993, Wraith et

al. 1995).

Differences in the Rate of Water Uptake after Drought

Following the first re-wet episode, the 15 cm depth had a water uptake rate 3 time higher

than at 7.5 cm in all communities. This difference may be partially explained by the

slower rate of dry-down at the 15 cm depth (data not shown). Therefore the roots at 7.5

cm had less water available for longer than those roots at 15 cm which caused damage

and a reduction water uptake rate.

87

Differences in expected root distribution between the three grass communities

were anticipated to create differences in near-surface water uptake. A majority of the root

system of the needle and thread - blue grama grass community occurs in the upper 15 cm

due to the prevalence of blue grama grass, while more of the root systems of crested

wheatgrass and Russian wildrye are found at greater depths (Coupland and Johnson

1965, Weaver 1958, Smoliak et al. 1972). Crested wheatgrass has a coarser, deeper root

system with a lower mass of roots in a given soil volume than the needle and thread -

blue grama grass community, while Russian wildrye is similar to crested wheatgrass but

having a greater horizontal spread (Weaver 1958, Smoliak and Johnston 1980, Dormaar

and Sauerbeck 1983, Smoliak and Dormaar 1985). However, in this study, there were no

differences in the rate of water uptake between communities at the two shallow soil

depths studied.

Arid and semiarid plants are adapted to drought through a variety of

physiological, morphological, phenological and life history strategies (Chesson et al.

2004, Schwinning et al. 2005a). The ability of blue grama grass to rapidly increase water

uptake by surviving roots, and development of new extensive fine root systems allows

absorption of water made available by short intense convection storms following drought

(Briske and Wilson 1977, Coyne and Bradford 1985, Johnson and Aguirre 1991). In

crested wheatgrass, potential water stress later in the season is often avoided through

early growth and development followed by senescence, and by hydraulic lift of deeper

sources of soil water and subsequent efflux into surface layers, thus reducing water stress

and root senescence near the soil surface (Caldwell et al. 1998, Hassanyar and Wilson

88

1978, Bittman and Simpson 1987, Bittman and Simpson 1989, Frank and Bauer 1991).


Crested wheatgrass and Russian wildrye monocultures resist invasion by other

species and have become a permanent part of North American grasslands with frequent

summer drought periods punctuated by short intense convection storms. This suggests

that these agronomic communities may possess adaptations that allow them to quickly

capitalize on water when it becomes available after a dry period. The study was

completed in a controlled environment greenhouse where crested wheatgrass, Russian

wildrye and Stipa-Bouteloua communities were established in large soil columns. Six

dry-down-then-rewetting sequences were initiated and soil water uptake rates were

determined by recording changes in soil water content hourly.

Although a previous study found differences in the rate of water uptake within

different genotypes of barley, the results of this study did not indicate any differences

between the agronomic monocultures and native mixed prairie grassland communities.

This lack of difference indicates that crested wheatgrass, Russian wildrye and native

communities are all well adapted to the semi-arid conditions and quickly absorb water

when it becomes available. Once established, crested wheatgrass and Russian wildrye

monocultures are able to compete as effectively for moisture as native communities

following intense convection storms, reducing colonization by other species and

maintaining a stable steady state community.

89

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Ares, J. 1975. Dynamics of the root system of blue grama. Journal of Range Management29(3): 208-213.

BassiriRad, H., and M.M. Caldwell. 1992. Temporal changes in root growth and 15Nuptake and water relations of two tussock grass species recovering from waterstress. Physiologia Plantarum 86:525-31.

Bittman, S., and G.M. Simpson. 1987. Soil water deficit effect on yield, leaf area, and netassimilation rate of three forage grasses: crested wheatgrass, smooth bromegrassand altai wildrye. American Society of Agronomy Journal 79:768-774.

Bittman, S., and G.M. Simpson. 1989. Drought effects on water relations of three culitvated grasses. Crop Science 29:992-999.

Briske, D.D., and A.M. Wilson.1977. Temperature effects on adventitious root development in blue grama seedlings. Journal of Range Management 30:276-280.

Caldwell, M., T. Dawson, and J. Richards. 1998. Hydraulic lift: consequences of water efflux from the roots of plants. Oecologia 113:151-161.

Chesson, P., R.L.E. Gebauer, S. Schwinning, N. Huntly, K. Wiegand, M.S.K. Ernest, A.Sher, A. Novoplansky, and J. Weltzin. 2004. Resource pulses, speciesinteractions, and viversity maintenance in arid and sem-arid environments.Oecologia 141: 236 -253.

Christian, J.M., and S.D. Wilson. 1999. Long-term ecosystem impacts of an introduced grass in the Northern Great Plains. Ecology 80(7):2397-2407.

Coupland, R.T. 1961. A reconsideration of grassland classification in the Northern Great Plains of North America. Journal of Ecology 49:135-167.

Coupland, R.T., and R.E. Johnson. 1965. Rooting characteristics of native grassland species in Saskatchewan. Journal of Ecology 53:475-507.

Coyne, P.I., and J.A. Bradford. 1985. Morphology and growth in seedlings of several C4 perennial grasses. Journal of Range Management 38:504-512.

Dormaar, J. F. 1978. Long-term changes associated with seed stands of crested wheatgrass in southeastern Alberta, Canada, p. 623-625. In: Proceedings of theFirst International Rangelands Congress. Denver, CO.

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Dormaar, J.F., and D.R. Sauerbeck. 1983. Seasonal effects on photoassimilated carbon-14 in the roots system of blue grama and associated organic matter. Soil Biologyand Biochemistry 15:475-479.

Frank, A.B., and A. Bauer. 1991. Rooting activity and water use during vegetative development of crested wheatgrass and western wheatgrass. Agronomy Journal 83:906-910.

Grime, J. 1994. The role of plasticity in exploring environmental heterogeneity, p. 1-18. In: M. Caldwell and R. Pearcy (EDS.). Exploitaton of enviromentalheterogeneity by plants. San Diego, CA: Academic Press.

Hassanyar, A.S., and A.M. Wilson. 1978. Drought tolerance of seminal lateral root apicesin crested wheatgrass and Russian wildrye. Journal of Range Management31:254-258.

Hook, P., and W. Lauenroth. 1994. Root system response of a perennial bunchgrass to neighborhood-scale water heterogeneity. Functional Ecology 8:738-745.

Hooper, D., and P. Vitousek. 1998. Effects of plant composition on nutrient cycling. Ecological Monographs 68:121-149.

Huang, B., and P.S. Nobel. 1993. Hydraulic conductivity and anatomy along lateral rootsof cacti: changes with soil water status. New Phytologist 123:499-507.

Johnson, D.A., and L. Aguirre. 1991. Effect of water on morphological development in three range grasses: root branching patterns. Journal of Range Management44:355-360.

Moss, E.H. 1944. The prairie and associated vegetation of southwestern Alberta. Canadian Journal of Resources 25(C):209-227.

Neumann, P.M. 1995. The resistance of cell walls adjustment in plant resistance to waterdeficits. Crop Science 35(5) 125801267.

North, G.B. and P.S. Nobel. 1991. Changes in hydraulic conductivity and anatomycaused by drying and re-wetting roots of Agave desert (Agavaceae).

Noy-Meir, I. 1973. Desert ecosystems: environment and producers. Annual Review of Ecology and Systematics 4:25-52.

SAS Institute, Inc. 2005. SAS OnlineDoc® 9.1.3. Cary, NC: SAS Institute Inc.

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Sala, O., and W. Lauenroth. 1982. Small rainfall events an ecological role in semiarid regions. Oecologia (Berlin) 53:301-304.

Sala, O.W., W.K. Lauenroth, W.J. Parton. 1982. Plant recovery following prolongeddrought in a shortgrass steppe. Agricultural Meteorology 27:49-58.

Sala, O.W.. Lauenroth, W.K. and W.J. Parton. 1992. Plant recovery following aprolonged drought in a short grass steppe. Ecology 73: 1175-1181.

Sheley, R., and L. Larson. 1995. Interference between cheatgrass and yellow star thistle seedlings. Journal of Range Management 47:470-474.

Sims, PL., Singh, J.A., and W.K. Lauenroth. 1978. The structure and function of tenwestern North American grasslands. Journal of Ecology 66:251–285.

Smoliak. S. 1956. Influence of climatic conditions on forage production of shortgrass rangeland. Journal of Range Management 9:89-91.

Smoliak S., and J.F. Dormaar. 1985. Productivity of Russian wildrye and crested wheatgrass and their effects on prairie soils. Journal of Range Management 38(5):403-405.

Smoliak, S., J.F. Dormaar, and A. Johnston. 1972. Long-term grazing effects on Stipa-Bouteloua prairie soils. Journal of Range Management 25(4):246-250.

Smoliak, S., and A. Johnston. 1980. Russian wildrye lengthens the grazing season. Rangelands 2(6):249-250.

Soon, W.K. 1988. Root distribution of and water uptake by field grown barley in a blacksoloed. Canadian Journal of Soil Science 68: 425-432.

Tilman, D., D. Walden, and J. Knows. 1996. Productivity and sustainability influencedby biodiversity. Nature (London) 379:718-720.

Topp, G.C., J.L. Davis and A.P. Annan. 1980. Electromagnetic determination of soil water content: measurements in coaxial transmission lines. Water Resource Research 16: 574-502

Weaver J. E. 1958. Summary and interpretation of underground development in natural grassland communities. Ecological Monographs 28(1):55-78.

Wraith, J.M. and J.M. Baker. 1991. High resolution measurement of root water uptakeusing automated time domain reflectometry. Soil Science Society of AmericaJournal 55: 928 - 932.

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Wraith, J.M., Baker, J.M. and T.K. Blake 1995. Water Uptake resumption following soildrought: a comparison among for barley genotypes. Journal of ExperimentalBotany 46(288): 873-880.

Wraith, J.M., and C.K. Wright. 1998. Soil water and root growth. In Proceedings of the Colloquim on the Soil Environment and Root Growth. 94th ASHS Annual Conference. Hortscience 33(6):951-959.

93

CHAPTER 6

COMPARATIVE WATER USE EFFICIENCY OF SELECTED NATIVE AND AGRONOMIC GRASS COMMUNITIES

Introduction

Water is limiting in grasslands in the Northern Great Plains, and the relationship

between soil water availability, atmospheric evaporative demand, and internal water

status modifies vegetative resource allocation and frequently limits production (Odum

1968, Brown 1977, Whitehead 1995). A number of researchers contend that competition

is intense in these arid and semiarid environments, and the ability of a species to be a

successful competitor is a function of more efficient use of scarce resources such as water

(Tilman 1982, Tilman 1988, Goldberg 1990, Busch and Smith 1995, Davis et al. 1998, Li

1999, Tsialtas et al. 2001). Others contend that increased competition is a result of less

efficient use of resources resulting in increased uptake which leaves less for competing

species (Gordon et al. 1989, Davis et al. 1998, Gordon et al. 1999). Both of these

mechanisms could inhibit the re-establishment of native communities after a disturbance

(Blicker et al. 2003).

Since the early 1900s, over two million hectares of native grassland in Canada

and the United States have been seeded to Agropyron cristatum (L.) Gaertn. (crested

wheatgrass) and Psathyrostachs juncea (Fisch.) Nevski (Russian wildrye) (Woolford

1951, Smoliak and Dormaar 1985). Native plant species have had little success in

94

invading these planted stands, allowing their continued existence as monoculture

alternate stable states (Heinrichs and Bolton 1950, Lawrence and Heinrichs 1977,

Knowles and Kilcher 1983, Redente et al. 1989). The inability of western wheatgrass

species to re-colonize may be a function of differences in water use efficiency (WUE),

which varies among species and is affected by climatic factors and plant and soil

characteristics (Briggs and Schantz 1914, Miller 1938, De Wit 1958, Stone and Stone

1975, Taylor et al. 1983, Frank et al. 1996, Abbate et al. 2004).

Above ground water use efficiency (WUE) research has been focused primarily

on annual crops rather than perennial grass species (Frank and Bauer 1991). This study

was undertaken to examine above ground WUE of two introduced perennial forage

monocultures (crested wheatgrass and Russian wildrye) and a Mixed Prairie (Stipa-

Agropyron-Bouteloua) community in a test of the hypothesis that persistence of these

monocultures is related to higher above ground water use efficiencies than for the native

Mixed Prairie communities.


Site Description of Source Plant Material

In 1997, nine plugs (40 cm diameter x 15 cm depth) were randomly selected from

native Mixed Prairie (western wheat - blue grama grass), crested wheatgrass and Russian

wildrye communities at the Animal Diseases Research Institute (ADRI) site near

Lethbridge, in south-central Alberta, Canada (49o 43' N, 110o 57' W). Crested wheatgrass

and Russian wildrye monocultures had been established at the ADRI site in 1993. This

95

site has a long-term annual average precipitation of 402 mm, with 76.5% falling from

April to September (Smoliak et al. 1967, Ellert and Janzen 1999). Soils at this site are

Orthic Dark Brown Chernozems (Typic Haploborolls). The 27 plugs were randomly

transplanted into steel column lysimeters (40 cm diameter x 120 cm depth) under a

rainout shelter at the Agriculture and Agrifood Canada Research Centre, Lethbridge,

Alberta (49o 42' N, 112o 42'W). Each lysimeter had been filled with sandy loam surface

horizon soil to a depth of 105 cm, packed in 15 cm intervals to a bulk density of 1.26 g

cm-3.

Experimental Design

The soil volumetric water content (2) of the sandy loam soil at -15 and -0.03 Mpa

mature potentials was determined using a pressure plate apparatus at the Lethbridge

Research Center. These were: 2 (-1.5 MPa) = 0.07 m3m-3 and 2 (-0.03 MPa) =0.18 m3m-3.

Throughout 1997, the column lysimeters were kept near -0.03 MPa by daily watering to

facilitate the establishment of the communities. In 1998, two water content regimes were

initiated within each with 4 replicates, the first at 2 = 0.07 and the second at 2 = 0.14.

Between May and September of 1998 and 1999, the lysimeters were weighed at two to

three day intervals using a 450 kg CM Loadstar electric winch, a load cell (ML 200), and

a digital weight recorder (DF 2000, Messload Technologies). Water was then added to

each lysimeter to restore treatment 2.

96

At the end of both growing seasons, the above ground biomass within each

lysimeter was harvested at a height of 2.5 cm, dried at 60" C for 48 hours, and weighed.

In the fall of 1999, the top 15 cm of soil was harvested from each lysimeter, as were two

5-cm diameter soil cores spanning 15-90 cm depth. The roots and crowns were double

washed using a 2-mm screen above a 0.5- mm screen to remove soil, dried at 60" C, and

weighed.

Above ground water use efficiency calculated as the total shoot mass produced by

plants (g) per unit of water (kg) used (Kramer and Boyer 1995) was determined for each

plant community for each year. Analysis of variance was performed using the MIXED

procedure of SAS statistical software (SAS Institute, Inc. 1999). Means separation was

achieved using least significant differences (LSD) (Steel and Torrie 1980), with

significance established as P < 0.05.

Weather records including precipitation, temperature, relative humidity, wind

speed, and Class A pan evaporation were obtained for April to August in 1998 and 1999

from a meteorological station adjacent to the rain-out shelter. Long-term weather records

for the site were secured from Lethbridge Research Center Agriculture and Agrifood

Canada.

Results

Environmental Conditions

Between 1998 and 1999 the potential evapotranspiration (PET) from April to

August was different in both pattern and amount. The total 1998 PET was near the long-

97

term average, but the monthly pattern was different, with April and June being much

lower and July and August much higher than average (Table 6.1). In 1999, the PET

pattern was similar to the long-term average, but the total was 26% higher, with monthly

totals being between 1.1 and 1.3 times the long-term averages (Table 6.1). The mean

monthly air temperatures from April to August 1998 were higher than the mean and than

1999 values except in June (Table 6.1). The mean relative humidity was lower than 1998

and 1999 values (Table 6.1). 1998 wind speeds were lower than 1999 and long-term

values during all five months (Table 6.1). Overall, April to September 1999 was cooler

than 1998, but windspeed and Class A Pan evaporation were higher (Table 6.1).

Above Ground Water Use Efficiency

Above ground WUE was not affected by 2 or by year main effects for any of the

grass communities. However, aerial biomass and total water used were affected by both

2 and year (Table 6.2).

Above ground WUE was greater in 1998 than 1999 only in the native Mixed

Prairie (needle and thread - wheatgrass - blue grama grass) community. In both years,

crested wheatgrass had greater above ground WUE than Mixed Prairie and Russian

wildrye (Table 6.3). In 1998, the aerial biomass was greater than for 1999 in all

communities. In 1998, crested wheatgrass aerial biomass was greater than that of Russian

wildrye, whereas there were no differences between communities in 1999 (Table 6.3).

Total water used in 1998 was greater than in 1999 in crested wheatgrass. In 1999, the

native community used more water than did crested wheatgrass (Table 6.3).

98

Table 6.1. Long-term average, 1998, and 1999 mean monthly air temperature, relativehumidity, wind speed, precipitation and Class A Pan Evaporation over thegrowing season at the Lethbridge Research Centre rainout shelter insouthern Alberta.

Year April May June July Aug.

Air Temperature (oC)

1998 7.8 13.6 14.4 20.3 20.1

1999 6.1 10.3 14.6 16.4 18.8

Ave.1 5.6 10.8 14.9 18.0 17.1

Relative Humidity (%)

1998 53.9 47.8 62.1 56.8 42.5

1999 49.5 48.3 54.5 54.0 54.2

Ave.1 44.0 40.0 40.0 38.0 38.0

Wind Speed (km h -1)

1998 13.7 16.0 15.0 12.7 12.5

1999 17.6 18.4 17.0 16.4 13.5

Ave.1 20.3 19.0 17.6 15.2 14.6

Precipitation (mm)

1998 41.9 53.4 148.4 57.4 36.2

1999 41.5 58.3 65.1 64.2 39.3

Ave.1 31.0 55.0 74.0 42.0 42.0

Class A Pan Evaporation (mm)

1998 0.0 213.2 190.5 319.6 309.5

1999 181.3 249.4 264.4 305.7 264.6

Ave.1 121.3 190.6 237.6 228.4 199.7

1 Long term averages - Agriculture and Agrifood Canada.

99

Table 6.2. Table of fixed effects for dry weight, total water used and water use efficiencyfor the lysimeter study of needle and thread - western wheat - blue gramagrass, crested wheatgrass, and Russian wildrye communities in soils with two different water content treatments in 1998 and 1999.

Effect Aerial Biomass Total Water Use Water Use Efficiency

-----------------------------------------------------Probabilities-----------------------------------------------------

Species 0.506 0.141 <0.001

Treatment <0.001 <0.001 0.130

Year <0.001 <0.001 0.064

Species x Treatment 0.414 0.035 0.126

Species x Year 0.024 0.186 0.376

Treatment x Year 0.086 0.119 0.328

Species x Treatment x Year 0.720 0.414 0.221

Table 6.3. Mean dry matter production (g), total water use (kg) and water use efficiency (g kg-1) in native (needle and thread grass - western wheat - blue grama grass),crested wheatgrass, and Russian wildrye communities in 1998 and 1999.

Variable Aerial Biomass (g) Total Water Use (kg) Water Use Efficiency (g kg-1)

Year 1998 1999 1998 1999 1998 1999

Species -------------------------------------------------------------------Means------------------------------------------------------------------

Native (NAT) 72.2 44.1* 60.1 45.2* 1.2 0.9*

Crested Wheatgrass(CWG)

78.3 41.4* 57.0 32.0* 1.5 1.5

Russian Wildrye (RWR) 56.5 41.5* 51.3 43.2 1.1 1.0

Contrasts ---------------------------------------------------------------Probabilities---------------------------------------------------------------

NAT vs CWG 0.572 0.799 0.604 0.030 0.050 <0.001

NAT vs RWR 0.139 0.804 0.140 0.736 0.583 0.564

CWG vs RWR 0.049 0.993 0.335 0.075 0.015 0.002

* Significant difference in treatment between years (P < 0.05).

100

Crown and Root Mass

There were higher root masses in the upper 15 cm of soil for crested wheatgrass

and native communities at 2 = 0.07 than at 2 = 0.14 (Table 6.4). Russian wildrye root

masses from 0 to 15 and 15 to 45 cm soil depths were greater than for the native

community at 2 = 0.07, but at 2 = 0.14 both Russian wildrye and native communities had

smaller root masses than crested wheatgrass (Table 6.4). There were no differences in 45-

90 cm depth and total root mass between soil water contents within communities.

Russian wildrye had a larger total root mass than the native community at 2 = 0.07m3 m-

3, while crested wheatgrass had larger total root mass than the native community at 2 =

0.14m3m-3 (Table 6.4).

Table 6.4. Total root mass and root mass for 0-15 cm, 0-45 cm, and 45-90 cm depths in native (needle and thread grass - wheatgrass - blue grama grass), crested wheatgrass, and Russian wildrye communities grown in a rain-out shelter under two soil moisture regimes at Lethbridge, Alberta, Canada in 1999.

0 - 15 cmDepth

0 - 45 cmSoil Water Content

45 - 90 cm Total (g)

0.07 0.14 0.07 0.14 0.07 0.14 0.07 0.14

Community ------------------------------------------------------------------Mean Root Mass (g) --------------------------------------------

Crested Wheatgrass (CWG) 163.7 216.7* 438.1 520.8 298.2 302.0 736.3 822.8

Native (NAT) 122.3 179.2* 323.0 365.2 260.3 262.0 583.4 627.2

Russian Wildrye (RWR) 174.7 146.6 449.9 419.4 358.1 345.3 807.9 764.7

Contrasts --------------------------------------------------------------Probabilities--------------------------------------------------------------

CWG vs NAT 0.102 0.117 0.038 0.007 0.554 0.533 0.130 0.057

RWR vs NAT 0.042 0.147 0.024 0.281 0.137 0.179 0.031 0.150

CWG vs RWR 0.653 0.008 0.821 0.052 0.353 0.477 0.293 0.533* There is a probability <0.05 between treatments.

The mass of root crowns were larger in Russian wildrye at 2 = 0.14 m3 m-3 than at

2= 0.07 m3 m-3, while differences in soil water content had no effect on the crown mass

101

of crested wheatgrass and native Mixed Prairie (Table 6.5). For 2 = 0.07, both crested

wheatgrass and Russian wildrye had larger crown masses than the native community,

while Russian wildrye had a larger crown mass than the other communities at 2 = 0.14

(Table 6.5).

Table 6.5. Mass of crowns at two different soil water contents (2) in crested wheatgrass,Russian wildrye and native Mixed Prairie (needle and thread grass - westernwheat - blue grama grass) grown in a rain-out shelter at the LethbridgeResearch Centre, Lethbridge, Alberta, Canada in 1998-1999.

Crowns (g m -2 ) (SE)1

2 = 0.07 2 = 0.14

Crested Wheatgrass (CWG) 122.0 (6.7) 109.0 (18.8)

Stipa-Agropyron-Bouteloua (NAT) 62.2 (11.5) 91.3 (14.2)

Russian Wildrye (RWR) 148.3 (1.5) 203.1( 14.4)*

Contrasts ------------------Probabilities ------------------

CWG vs NAT 0.005 0.338

RWR vs NAT <0.001 <0.001

CWG vs RWR 0.182 <0.001

* There is a significant difference (P < 0.05) between different soil water contents 1 The means are followed by the standard error of the mean in brackets

Discussion

The Effect of Water Content on Roots, Crownsand Above Ground Water Use Efficiency

In semi-arid northern grassland communities, most native plants possess

adaptations to water stress, such as phenological modifications, stomatal control,

morphological modifications, root systems that are able to respond to physiological

demands, alternate photosynthetic pathways, osmotic adjustments and dehydration

102

tolerance mechanisms (Brown 1995). In these native communities, partitioning of limited

environmental resources by potentially competing organisms as a result of structural or

functional differences allows coexistence of species and creates long-term stability

(Whittaker 1969, Whittaker et al. 1973).

The two soil water content treatments used did not result in differences in water

use efficiency within the perennial grass communities studied. Previous work with C3

species has shown reductions (Heitholt 1989), increases (Johnson et al. 1990), and lack of

differences (Johnson and Bassett 1991, Xue et al. 2003, Zhang et al. 1998) in above

ground WUE in response to differences in soil water content. Although C4 species such

as Bouteloua gracilis (Wild. ex Kunth) Lag ex Griffiths (blue grama) and Artemisia

frigida Willd. (pasture sagewort) have higher inherent above ground WUE than C3

grasses (Akhter et al. 2003), their small contribution to the aerial biomass of the native

community at ADRI as determined by Willms et al. (1993), would presumably have had

little effect on above ground WUE.

The three grass communities had different root system responses in relation to the

two soil water content treatments. Although there was no overall difference in total root

mass between 2 = 0.07 and 2 = 0.14 in any of the communities, crested wheatgrass and

native communities had smaller root masses between 0-15 cm depths at 2 = 0.07,

whereas there was no difference in Russian wildrye, indicating that near-surface root

mass of crested wheatgrass and native Mixed Prairie communities were negatively

impacted by low season-long soil water content whereas the increased surface root mass

of Russian wildrye may be an adaptation to those conditions. Crested wheatgrass and

103

Russian wildrye were able to maintain crown mass at the lower soil water content.

Carbohydrates may be translocated to the crown for storage to facilitate osmotic

adjustment (Chaves 1991, Frank and Bauer 1991), thus preventing crown senescence and

providing materials for regrowth of roots when conditions become more favourable.

Above Ground WUE

Crested wheatgrass demonstrated a higher above ground WUE than Russian

wildrye or native Mixed Prairie communities due to utilization of less water rather than

production of greater standing crop. Above ground WUE values reported in the present

study are at the lower limit of the ranges (1 to 3 g kg-1) reported by Kramer and Boyer

(1995) and Blicker et al. (2003). There are a number of explanations that may account for

the lower values observed in this study. First, most of the previous studies were

conducted in Utah and the more northerly location of this study may have constrained

aerial production due to lower light intensity, air and soil temperatures. Secondly, most of

the previous studies considered annual agronomic species selected for high above ground

production. Finally, the reduction of fallen and standing litter with harvest may have

increased evapotranspiration (Willms, 1988, Willms 1993).

Crested wheatgrass, a cool season bunchgrass, has greater root mass in the upper

45 cm, which may result in rapid uptake of water from this layer early in the growing

season when temperatures, potential evaporation, and water vapour pressures are lower

than they are later in the season. This results in early development of aerial biomass and

higher above ground WUE (Smika et al. 1965, Bittman 1985, Frank et al. 1996). Later in

the season (July and August), when soil water availability is lower and evaporative

104

demand is higher, leaf rolling and dormancy reduce transpiration losses by this grass

(Bittman and Simpson 1989).

Higher water use efficiency does not necessarily confer high drought resistance

(Johnson and Bassett 1991), but in these perennial grasses this characteristic in concert

with higher soil nitrate concentration immediately after cultivation (Porter, Chapter 4)

may allow establishment and maintenance of these monoculture communities. The

efficient use of water may limit the germination of native grass seeds that are not

numerous in the seed back and have very narrow germinations requirements (Lauenroth

et al. 1994, Coffin et al. 1996, Heidinga and Wilson 2002).


Crested wheatgrass demonstrated a higher WUE than either Russian wildrye or

native Mixed Prairie communities by utilizing less water to produce a similar quantity of

above ground biomass. WUE values reported in the study are at the lower limit of the

ranges reprted by others. This field research was conducted in southern Alberta, Canada

where lower growing season light intensity, air and soil temperatures in addition to high

winds may have constrained production. In addition, harvesting at the end of each

growing season reduced soil surface litter and may have increased evaporation.

Although above ground biomass was not different between these communities,

there were differences in quantity of crown and root mass at the lower soil water content.

Russian wildrye had a larger total root mass than the native grassland community which

was due to a greater root mass near the soil surface. This suggests that Russian wildrye is

105

able to more effectively explore surface layers for water when it is less available. Both

agronomic species maintained larger crown masses when soil water content was lower.

During that period nutrients may be translocated to the crown to allow faster regrowth of

roots when moisture levels are more favourable. However the root mass in crested

wheatgrass was not larger than the native community, suggesting greater growth of root

mass when soil water content is higher.

These two introduced grass communities seem to have different methods of

adapting to semi-arid conditions. The higher WUE coupled with the larger crown mass of

crested wheatgrass may allow rapid root and shoot growth in the spring, and Russian

wildrye may better utilize moisture near the soil surface throughout the growing season.

In addition to these adaptations, rapid utilization of nitrate released in cultivation and

higher water use efficiencies may sustain these monocultures. Although native species

may have some of the same adaptations, lower water use efficiencies, low soil nitrate

after cultivation and the absence of a high concentration of viable seeds in the seed-bed

of these monocultures, may limit re-colonization.

106

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CHAPTER 7

SUMMARY

This project was initiated to investigate changes in nitrogen partitioning and water

dynamics in the first four years after plowing and seeding native grasslands in the

northen Great Plains of southern Alberta, Canada to annual and perennial agronomic

species. The objectives of this research were to evaluate 1) short-term changes in soil N

partitioning created by cultivating and seeding native grasslands with selected annual

(wheat) and perennial (crested wheatgrass and Russian wildrye) monocultures; 2)

changes in partitioning of N within the biomass of these selected species; 3) difference in

the rate of water uptake between Mixed Prairie grasslands, crested wheatgrass and

Russian wildrye after a dry-down period; and 4) differences in above ground water use

efficiency, root and crown masses between Mixed Prairie grasslands, crested wheatgrass

and Russian wildrye under two soil water content levels.

The research for Objectives 1 and 2 relating to short-term changes in soil and

plant N in annual and perennial monocultures was conducted in 1995 and 1997 at three

locations in the northern Great Plains (Onefour, Lethbridge and Stavely, Alberta) with

different soils, climate and native plant communities. Objective 3 relating to rates of

water uptake after a dry-down period by native needle and thread - blue grama grass,

crested wheatgrass and Russian wildrye communities was evaluated in 1998, using

horizontal TDR probes placed at three depths in columns at a controlled environment

112

greenhouse at Montana State University. The fourth study relating to the determination

of above ground water use efficiency, root and crown masses under two soil water

contents was conducted in 1998 and 1999, using weighing column lysimeters under a

rain-out shelter at the Lethbridge Research Centre in Lethbridge, Alberta, Canada. The

column lysimeters contained crested wheatgrass, Russian wildrye and the native Mixed

Prairie (needle and thread-native wheatgrass - blue grama grass) communities. Two

different water contents were imposed on the communities and total water used during

the growing season was recorded for each year of the study. Shoot mass was harvested at

the end of each growing season and root and crown mass was harvested at the end of the

study. Above ground WUE was calculated for the two growing seasons.

N sequestered as biomass, soil N, LF and LFN in native grassland communities

increased with increases in long-term annual precipitation. A large proportion of biomass

N was sequestered by root mass in the perennial monocultures and native grasslands. All

of the native grassland systems studied were dominated by ammonium N sources rather

than nitrate.

In the short-term, cultivation and seeding of native grasslands had no effect on

total soil N, due to a large reservoir of N in soil organic matter. However, these activities

reduced the light fraction and light fraction N in the soil. This was presumably caused by

increased mineralization which produced an increase in the concentration of nitrate

(NO3-) in the soil. After 4 years, losses in the light fraction N in soil under wheat

treatments were greater than 60%, with the largest losses occurring at the site with the

highest long-term annual precipitation. Soil nitrate under wheat remained higher than

113

observed in either perennial monocultures or native grasslands. Losses in the light

fraction and light fraction N were not as great under perennial agronomic monocultures,

but the LF and LFN were smaller in these perennials than in native communities.

Larger losses in light fraction (LF) and LFN under wheat than perennial

monocultures, in the short-term, is a function of the frequency of cultivation and

differences in the size of the root masses. Losses in LF and LFN of annual and perennial

monocultures will continue until new equilibria are established with the reduction being

more rapid with above average precipitation. The new equilibrium under wheat will be

dependent on cropping system but in any case losses will be greater under perennial grass

monocultures.

Annual agronomic monocultures sequester less N into biomass than either native

or cultivated perennial communities, even with increased nitrate available for absorption.

This is likely due to their inability to accommodate N above basic requirements for

growth. Due this inability, some of the increased soil nitrate available due to accelerated

mineralization will be lost through a combination of volatilization, leaching and runoff.

Most of N absorbed is assimilated in leaves, translocated to the seed heads and removed

during harvest. The rate and quantity of losses in soil nitrate under annual monocultures

will be a function of both climate and the variability of soil moisture and temperature

regimes during the growing season. Generally, the warmer and wetter the growing

season, the more rapid the loss.

114

The lower reduction in LF and LF N under perennial monocultures compared to

wheat was likely a product of both higher root mass and only a single cultivation in the

case of the perennials. However, soil nitrate levels were not elevated as was observed in

wheat. The single pulse of nitrate resulting from the single cultivation event and the

perennial bunchgrass form of these species may have facilitated greater absorption of N

and lower soil nitrate concentrations. Orchardgrass in 1995 was an exception to this

pattern, and the difference may have been a result of root death caused by drought the

two previous years.

Although perennial monocultures have been selected for increased aerial

production, in this study only crested wheatgrass and smooth brome grass had

significantly higher shoot masses than native communities. However, lower shoot mass N

concentration in these species resulted in lower total N in shoot mass than native

communities, except with crested wheatgrass at the Stipa-Bouteloua site in 1995. This

was likely a result of a combination of a more recent establishment date and increased

current growing season precipitation. Therefore, although the establishment of perennials

limits the frequency of cultivation, species like crested wheat grass and Russian wildrye

with lower R:S and lower N concentration in root mass will create larger N losses from

the system through harvest. During periods of high current growing season precipitation

the concentration of N in shoot mass was higher in crested wheatgrass and smooth

bromegrass suggesting that during moist years, harvesting of crested wheatgrass and

bromegrass will further increase N losses from the system.

115

In the short-term, cultivation and seeding of native grasslands to annual and

perennial monocultures changes N partitioning in the plant-soil complex. The magnitude

of the change rather the ranking of the change within treatments is determined by

differences in long-term and current precipitation. Perennial monocultures maintained

light fraction N better than annual monocultures. However, it is likely that management

practices will modify the magnitude of the differences between annual and perennial

monocultures. Differences will be smaller with no-till continuous cropping systems in

annuals versus over-harvested or grazed perennial forages.

Differences in root distribution between native communities and agronomic

monocultures were expected to create differences in the rate of water uptake after a period

of soil water depletion. However, after artificially imposed periods of water stress, there

were no differences in the rate of water uptake between Stipa-Bouteloua, crested

wheatgrass, and Russian wildrye. This suggests that these two introduced species which

evolved in ecosystems with similar quantities and variability in water supply are as well

adapted to rapid absorption of water as the native communities. This characteristic is

likely important in maintaining these introduced monocultures as alternate steady state

communities.

Crested wheatgrass possessed a higher water use efficiency than either Russian

wildrye or native (Stipa-Agropyron-Bouteloua) communities due to the utilization of less

water rather than greater production of aerial biomass. The values obtained in this

research were near the lower limit of the ranges reported by other researchers. The

differences reported here may be partially due to the fact that this study was conducted

116

further north, commensurate with lower light intensities and lower air and soil

temperatures, which may have constrained production. In addition, these perennial species

partition more nutrients to crowns and roots therefore reducing above ground WUE.

This research adds to our understanding of the roles that water and nitrogen may

play in the maintenance of alternate steady state communities that are produced after

disturbances such as cultivation. The interrelationship between water and a single pulse

of soil nitrate created by a disturbance such as cultivation may allow crested wheatgrass

and Russian wildrye to absorb and assimilate the excess mineral N. Later in the year

when water is not as available, the N in shoot mass will be translocated out of leaves and

stems and into seed heads, crown and roots. The N translocated into the crown and roots

may allow more rapid re-growth and allow preemption of soil water and N before other

possible colonizing species. This may be one of the reasons that these monocultures

survive over the long term.

Since large volumes of water are used by these monocultures to produce a large

standing crop early in the growing season, it is expected that heavy removal of leaves

through grazing or other means early in the season when the crowns are just beginning to

produce new tillers, and continuing removal over the length of the growing season, will

over time damage roots and crowns. This may provide a window of opportunity for

colonization by other species with highly viable seeds, capable of rapid germination and

establishment, and with high water use efficiencies. But if not properly managed, many

may not be native nor desirable. It may require substantial time and effort to re-establish

multispecies native communities within these monocultures. These activities may include

117

extensive leaf removal, herbicide, water and fertilizer application, and the provision of

highly viable seed.

118

APPENDICES

119

APPENDIX A

NITROGEN PARTITIONING TABLES IN CHAPTER 3

120

Table 3.1. Monthly growing season precipitation (mm) and temperatures (ºC) from 1995 to 1997 at three southern Alberta sites.

Mean Monthly Temperatures (ºC)


Stipa-Bouteloua

1995 -1.200 3.600 10.800 15.800 18.000 17.600 13.000 11.100 97.900

1997 -1.500 3.600 11.400 16.600 19.300 19.600 15.700 12.100 106.800

Ave. 2 -2.900 5.200 11.400 15.600 19.600 18.800 12.200 11.300 100.000


1995 -0.300 4.300 10.100 14.600 17.300 15.800 12.500 10.600 96.300

1997 0.700 3.900 11.300 16.000 18.200 18.600 15.900 12.100 109.700

Ave. 2 -1.500 5.600 10.800 14.900 18.000 17.100 12.200 11.000 100.000

Festuca-Danthonia3

1995 -1.400 3.700 9.200 14.100 16.100 15.000 11.900 9.800 104.400

1997 -2.000 2.000 8.800 12.900 15.500 16.300 14.300 9.700 103.200

Ave. 2 -2.100 5.000 8.700 12.800 15.700 15.200 10.400 9.400 100.000

1 % - Sum of precipitation and temperatures from March to September divided by the long-term averages during the same period. 2 Long-term averages - Agriculture and Agri-food Canada. 3 Measured at Claresholm.

121

Table 3.2. Total model for total biomass, shoot mass, root mass, root:shoot (R:S), concentration N in shoot mass, concentration N in root mass, shoot mass N, root mass N. total N in biomass and R:S N of native and agronomiccommunities at three southern Alberta sites in 1995 and 1997.

Biomass

(g m-2)

Shoot Mass

(g m-2)

Root Mass

(g m-2)

Root:Shoot Concentration Shoot N(mg g-1)


Shoot N

(g m-2)

Root N

(g m-2)

Total N

(g m-2)

R:S N

Source ---------------------------------------------------------------------------------------------------Probabilities-------------------------------------------------------------------------------------------------Year (Y) 0.196 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.008 0.001Site (S) <0.001 <0.001 <0.001 0.015 0.070 0.031 <0.001 <0.001 <0.001 <0.001Treatment (T) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001S x Y 0.552 0.003 0.179 0.114 <0.001 <0.001 0.030 0.077 0.085 0.186T x Y <0.001 <0.001 0.004 0.010 <0.001 0.006 <0.001 0.018 <0.001 0.006T x S <0.001 0.010 0.001 0.003 <0.001 <0.001 <0.001 <0.001 <0.001 0.002S x Y x T 0.384 0.005 0.674 0.228 <0.001 0.224 0.003 0.667 0.629 0.527Site --------------------------------------------------------------------------------------------------------Means----------------------------------------------------------------------------------------------------Stipa-Bouteloua

Native 1015.300 66.900 948.400 15.400 1.100 1.400 0.700 14.100 14.800

Perennial Grass1 943.200 183.100 760.100 6.200 1.100 1.400 1.800 11.000 12.800Wheat2 987.800 503.900 483.900 1.200 0.700 1.600 3.800 8.100 12.000Stipa-Bouteloua-Agropyron

Native 1135.700 181.200 1033.500 8.300 1.300 1.300 2.100 14.200 16.300Perennial Grass1 1152.900 203.300 1022.200 6.600 0.900 1.200 1.600 12.100 13.700Wheat2 809.700 524.200 306.400 1.100 0.800 1.600 3.800 5.100 8.900Festuca-Danthonia

Native 2153.200 265.000 1888.000 7.300 1.200 1.500 3.000 30.900 34.000Perennial Grass3 1731.100 389.900 1341.200 6.600 1.000 1.300 3.500 17.300 20.800Wheat2 1030.200 556.300 473.800 1.500 0.700 1.400 3.800 6.500 10.400

1 Crested wheatgrass and Russian wildrye.2 Fallow and continuously cropped wheat. 3 Smooth bromegrass and orchardgrass.

122

Table 3.3. Partial model of probabilities of differences between sites in total biomass, shoot mass, root mass, R:S, concentration N in shoot mass, concentration N in root mass, shoot mass N, R:S N of native and agronomic communities at three southern Alberta sites in 1995 and 1997.

Biomass

(g m-2)

Shoot Mass

(g m-2)

Root Mass

(g m-2)

Root: Shoot Concentration Shoot N(mg g-1)


Shoot N

(g m-2)

Root N

(g m-2)

Total N

(g m-2)

R:S N

Site ---------------------------------------------------------------------------------------------------Probabilities-----------------------------------------------------------------------------------------------

--

Stipa-Bouteloua

Treatment (T) 0.059 <0.001 <0.001 <0.001 <0.001 0.017 <0.001 <0.001 0.015 <0.001

Year (Y) 0.100 <0.001 0.017 0.004 <0.001 0.834 <0.001 0.063 0.222 <0.001

T x Y <0.001 <0.001 0.670 0.429 <0.001 0.197 <0.001 0.102 0.003 0.386

Stipa-Bouteloua-Agropyron

Treatment (T) <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.002

Year (Y) 0.189 <0.001 <0.001 <0.001 0.053 <0.001 <0.001 <0.001 <0.001 <0.001

T x Y <0.001 <0.001 <0.001 0.011 0.388 0.002 <0.001 <0.001 <0.001 0.087

Festuca-Danthonia

Treatment (T) <0.001 <0.001 <0.001 <0.001 <0.001 0.029 <0.001 <0.001 <0.001 <0.001

Year (Y) 0.010 <0.001 0.032 0.089 <0.001 0.159 <0.001 0.051 0.444 0.038

T x Y 0.020 <0.001 0.152 0.677 <0.001 0.127 <0.001 0.294 0.098 0.141

123

Table 3.4. The total biomass and root:shoot mass production (R:S) of agronomic and native communities in three selected sites in southern Alberta in 1995 and 1997.

Site Stipa-Bouteloua Stipa-Agropyron-Bouteloua Festuca-Danthonia

Total Biomass(g m-2)

R:S Total Biomass(g m-2)

R:S Total Biomass(g m-2)

R:S

Year 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment --------------------------------------------------------------------------------------------------------Means---------------------------------------------------------------------------------------------------

Native (NAT) 847.100 1183.500 12.800 18.100* 847.200 1424.300 2.400 14.300* 1700.300 2606.000 6.300 8.300

Crested Wheatgrass (CWG) 1071.300 1013.300 1.900 5.800 1050.900 1304.200 1.700 6.400* - - - -

Smooth Brome (B)2 - - - - - - - - 1741.700 2124.500 1.200 4.400

Russian Wildrye (RWR) 793.100 895.100 7.200 10.000 870.300 1386.600* 4.900 13.800* - - - -

Orchardgrass (D)2 - - - - - - - - 1404.900 1653.300 5.100 15.600*

Wheat Continuous (WC)1 1074.500 720.900* 0.600 2.300 866.400 622.800* 0.400 2.500 1017.500 710.300 0.900 3.700

Wheat Fallow (WF)1 1328.200 827.500* 0.800 1.300 1268.200 481.300* 0.200 1.200 1759.200 633.700* 0.600 0.900

Contrast ---------------------------------------------------------------------------------------------------Probabilities-------------------------------------------------------------------------------------------------

NAT vs CWG 0.083 0.183 <0.001 <0.001 0.062 0.276 0.136 <0.001 - - - -

NAT vs B - - - - - - - - 0.910 0.195 0.096 0.189

NAT vs RWR 0.669 0.028 0.018 0.015 0.828 0.722 0.265 0.825 - - - -

NAT vs D - - - - - - - - 0.423 0.014 0.692 0.020

CWG vs RWR 0.034 0.352 0.018 0.064 0.097 0.439 0.150 0.002 - - - -

B vs D - - - - - - 0.362 0.205 0.197 <0.001

NAT vs WC 0.079 <0.001 <0.001 <0.001 <0.001 <0.001 0.356 <0.001 0.070 <0.001 0.075 0.122

NAT vs WF <0.001 0.008 <0.001 <0.001 <0.001 <0.001 0.295 <0.001 0.872 <0.001 0.062 0.017

WC vs WF 0.051 0.400 0.899 0.619 <0.001 0.189 0.898 0.562 0.050 0.835 0.926 0.353 1 - Wheat continuous was planted each year and fallow wheat was planted every alternate year. 2 - NOTE:At the Festuca-Danthonia site, bromegrass and orchardgrass were substituted for crested wheatgrass and Russian wildrye. *.- There is a significant difference in treatment between years (P<0.5).

124

Table 3.5. Biomass of shoot and roots of native and agronomic communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.

Shoot Biomass (g m-2) Root Biomass (g m-2)

Site Stipa-Bouteloua Stipa-Agropyron-Bouteloua

Festuca-Danthonia Stipa-Bouteloua Stipa-Agropyron-Bouteloua

Festuca-Danthonia

Year 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment -------------------------------------------------------------------------------------------------------------Means-------------------------------------------------------------------------------------------------------

Native (NAT) 65.500 71.300 223.000 109.200* 248.600 281.700 784.600 1112.200* 594.100 1315.100* 1451.700 2324.300*Bromegrass (B) -- -- -- -- 801.500 389.500* -- -- -- -- 940.200 1735.200*

Crested Wheatgrass (CWG)

394.000 159.300* 392.300 177.800* -- -- 677.400 854.000 658.500 1226.200 -- --

Orchardgrass (D) -- -- -- -- 238.300 130.200 -- -- -- -- 1166.100 1523.100

Russian Wildrye (RWR)

97.400 81.700 150.100 93.200* -- -- 695.700 813.400 720.200 1293.400 -- --

Wheat Continuous (WC)

694.500 226.600* 610.600 182.700* 544.500 166.000* 380.100 494.300 255.700 440.000 473.000 544.300

Wheat Fallow (WF) 682.300 365.600* 1081.700 222.100* 1179.600 335.400* 599.500 461.900 186.500 259.500 579.700 298.300

Contrasts --------------------------------------------------------------------------------------------------------Probabilities--------------------------------------------------------------------------------------------------------

NAT vs CWG <0.001 0.084 0.002 0.189 -- -- 0.036 0.015 0.541 0.052 -- --NAT vs B -- -- -- -- <0.001 0.203 -- -- -- -- 0.167 0.113NAT vs RWR 0.519 0.834 0.163 0.756 -- -- 0.053 0.005 0.236 0.817 -- --NAT vs D -- -- -- -- 0.906 0.078 -- -- -- -- 0.435 0.034CWG vs RWR <0.001 0.126 <0.001 0.108 -- -- 0.856 0.686 0.558 0.083 -- --B vs D -- -- -- -- <0.001 0.005 -- -- -- -- 0.536 0.561NAT vs WC <0.001 0.004 <0.001 0.160 0.002 0.172 <0.001 <0.001 0.003 <0.001 0.011 <0.001NAT vs WF <0.001 <0.001 <0.001 0.035 <0.001 0.519 0.006 <0.001 <0.001 <0.001 0.022 <0.001WC vs WF 0.807 0.008 <0.001 0.447 <0.001 0.051 0.035 0.747 0.511 0.063 0.770 0.500

*.- There is a significant difference in treatment between years (P < 0.5).

125

Table 3.6. Total biomass N of native and agronomic communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.

Total Biomass N (g m-2) R:S N



Festuca-Danthonia

Year 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment -------------------------------------------------------------------------------------------------Means--------------------------------------------------------------------------------------------

Native (NAT) 12.800 16.700* 10.000 22.600* 26.500 41.400* 17.300 24.400 2.700 17.900* 7.700 13.500

Bromegrass (B) -- -- -- -- 21.400 23.300 – – – – 2.000 10.000*

Crested Wheatgrass (CWG) 13.200 13.100 9.100 17.400* -- -- 3.100 15.200* 2.700 13.900* – --

Orchardgrass (D) -- -- -- -- 17.300 21.300 – – – – 5.000 16.900*

Russian Wildrye (RWR) 12.400 12.600 9.200 19.300* -- -- 5.500 13.900* 4.500 16.000* -- --

Wheat Continuous (WC) 10.800 9.500 8.300 10.500 10.600 8.900 1.100 9.100* 0.700 7.200* 2.000 8.300

Wheat Fallow (WF) 17.700 10.100* 9.400 7.500 15.500 9.600 1.600 3.300 0.400 3.200 0.800 2.200

Contrasts --------------------------------------------------------------------------------------------Probabilities------------------------------------------------------------------------------------------

NAT vs CWG 0.848 0.054 0.568 0.005 -- -- <0.001 0.012 0.999 0.230 -- --

NAT vs B -- -- -- -- 0.392 0.005 -- -- -- -- 0.047 0.224

NAT vs RWR 0.826 0.030 0.944 0.292 -- -- 0.003 0.072 0.579 0.565 -- --

NAT vs D -- -- -- -- 0.129 0.002 -- -- -- -- 0.335 0.019

CWG vs RWR 0.671 0.787 0.617 0.058 -- -- 0.499 0.725 0.579 0.524 -- --

B vs D -- -- -- -- 0.492 0.727 -- -- -- -- 0.279 0.002

NAT vs WC 0.279 <0.001 0.311 <0.001 0.011 <0.001 <0.01 <0.001 0.540 0.003 0.049 0.074

NAT vs WF 0.012 0.001 0.725 <0.001 0.070 <0.001 <0.001 <0.001 0.479 <0.001 0.019 <0.001

WC vs WF <0.001 0.758 0.504 0.092 0.414 0.706 0.874 0.119 0.922 0.214 0.670 0.040*.- There is a significant difference in treatment between years (P < 0.5).

126

Table 3.7. Concentration N in net shoot and root mass of native and agronomic communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.

Shoot Biomass Concentration N (mg g-1) Root Biomass Conentration N (mg g-1)



Festuca-Danthonia

Year 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment ----------------------------------------------------------------------------------------------------Means-------------------------------------------------------------------------------------------------

Native (NAT) 1.100 1.100 1.200 1.300 1.300 1.000* 1.400 1.400 1.200 1.500* 1.400 1.600

Bromegrass (B) -- -- -- -- 0.900 0.500* -- -- -- -- 1.400 1.200

Crested Wheatgrass (CWG) 0.900 0.600* 0.600 0.700 -- -- 1.500 1.400 1.000 1.300* -- --

Orchardgrass (D) -- -- -- -- 1.300 1.200 -- -- -- -- 1.200 1.300

Russian Wildrye (RWR) 2.000 1.100* 1.100 1.200 -- -- 1.500 1.400 1.000 1.300* -- --

Wheat Continuous (WC) 0.800 0.400* 0.800 0.800 0.600 0.600 1.500 1.700* 1.300 1.900* 1.500 1.400

Wheat Fallow (WF) 0.900 0.700* 0.600 0.900 0.800 0.800 1.700 1.700 1.400 1.900* 1.200 1.500*

Contrasts ------------------------------------------------------------------------------------------------Probabilities---------------------------------------------------------------------------------------------

NAT vs CWG <0.001 <0.001 <0.001 <0.001 -- -- 0.439 0.666 0.003 0.092 -- --

NAT vs B -- -- -- -- <0.001 <0.001 -- -- -- -- 0.929 0.004

NAT vs RWR <0.001 0.947 0.318 0.329 -- -- 0.181 0.963 0.013 0.033 -- --

NAT vs D -- -- -- -- 0.036 <0.001 -- -- -- -- 0.066 0.012

CWG vs RWR <0.001 <0.001 <0.001 <0.001 -- -- 0.560 0.700 0.548 0.605 -- --

B vs D -- -- -- -- <0.001 <0.001 -- -- -- -- 0.079 0.658

NAT vs WC <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.434 0.017 0.186 <0.001 0.834 0.163

NAT vs WF 0.002 <0.001 <0.001 <0.001 <0.001 <0.001 0.004 0.023 0.022 <0.001 0.141 0.320

WC vs WF 0.002 <0.001 0.108 0.288 0.005 0.870 0.026 0.898 0.292 0.340 0.095 0.678*.- There is a significant difference in treatment between years (P<0.5).

127

Table 3.8. Total N in net shoot and root mass of native and agronomic communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.

Shoot Biomass N Root Biomass N



Festuca-Danthonia

Year 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment ----------------------------------------------------------------------------------------------------------Means---------------------------------------------------------------------------------------------------

Native (NAT) 0.700 0.800* 2.800 1.500* 3.300 2.800 12.100 16.000* 7.200 21.200* 23.600 38.600*

Bromegrass (B) -- -- -- -- 9.400 2.100* -- -- -- -- 14.000 21.200

Crested Wheatgrass (CWG) 3.400 0.900* 2.500 1.200* -- -- 9.800 12.200 6.600 16.300* -- --

Orchardgrass (D) -- -- -- -- 3.000 1.500* -- -- -- -- 14.300 19.800

Russian Wildrye (RWR) 1.900 0.900* 1.700 1.100 -- -- 10.500 11.700 7.500 18.100* -- --

Wheat Continuous (WC) 5.300 1.000* 5.000 1.500* 3.400 1.000* 5.500 8.500* 3.300 9.000* 7.100 7.900

Wheat Fallow (WF) 6.500 2.400* 6.900 2.000* 8.800 2.100* 10.500 7.700 2.600 5.500 6.600 7.500

Contrasts ------------------------------------------------------------------------------------------------------Probabilities-----------------------------------------------------------------------------------------------

NAT vs CWG <0.001 0.784 0.534 0.541 -- -- 0.190 0.041 0.716 0.008 -- --

NAT vs B -- -- -- -- <0.001 0.224 -- -- -- -- 0.128 0.006

NAT vs RWR 0.006 0.783 0.026 0.474 -- -- 0.366 0.022 0.874 0.087 -- --

NAT vs D -- -- -- -- 0.614 0.054 -- -- -- -- 0.143 0.003

CWG vs RWR <0.001 0.999 0.096 0.917 -- -- 0.674 0.780 0.602 0.282 -- --

B vs D -- -- -- -- <0.001 0.373 -- -- -- -- 0.954 0.803

NAT vs WC <0.001 0.003 <0.001 0.969 0.884 0.011 <0.001 <0.001 0.030 <0.001 0.011 <0.001

NAT vs WF <0.001 <0.001 <0.001 0.244 <0.001 0.273 0.356 <0.001 0.011 <0.001 0.009 <0.001

WC vs WF 0.007 0.002 <0.001 0.259 <0.001 0.113 0.009 0.652 0.667 0.051 0.930 0.577*.- There is a significant difference in treatment between years (P<0.5).

128

Table 3.9. Carbon to nitrogen ratios (C:N) of shoot and root mass of native and agronomic communities at Stipa-Bouteloua, Stipa-Agropyron-Bouteloua, and Festuca-Danthonia sites in southern Alberta in 1995 and 1997.

Shoot Biomass C:N Root Biomass CN



Festuca-Danthonia

Year 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment ----------------------------------------------------------------------------------------------------------Means---------------------------------------------------------------------------------------------------

Native (NAT) 40.900 43.400 36.900 35.400 33.600 45.200 30.600 32.000 37.300 30.900 25.000 24.900

Bromegrass (B) -- -- -- -- 49.300 84.500 -- -- -- -- 27.700 30.600

Crested Wheatgrass (CWG) 53.700 83.000 71.100 69.400 -- -- 28.200 33.400 45.900 35.000 -- --

Orchardgrass (D) -- -- -- -- 33.600 37.700 -- -- -- -- 31.000 30.300

Russian Wildrye (RWR) 23.500 43.800 38.500 37.400 -- -- 27.800 32.400 42.100 35.900 -- --

Wheat Continuous (WC) 60.100 104.300 27.800 62.800 74.000 77.700 30.500 26.900 34.900 25.800 28.700 26.700

Wheat Fallow (WF) 48.900 70.800 72.800 58.100 62.300 73.400 24.600 27.800 32.900 25.100 29.000 27.900

Contrasts -----------------------------------------------------------------------------------------------------Probabilities------------------------------------------------------------------------------------------------

NAT vs CWG -- <0.001 -- <0.001 -- -- 0.357 0.598 <0.001 0.053 -- --

NAT vs B -- -- -- -- -- <0.001 -- -- -- -- 0.314 0.040

NAT vs RWR -- 0.944 -- 0.772 -- -- 0.300 0.867 0.024 0.019 -- --

NAT vs D -- -- -- -- -- <0.001 -- -- -- -- 0.031 0.050

CWG vs RWR -- <0.001 -- <0.001 -- -- 0.905 0.718 0.070 0.650 -- --

B vs D -- -- -- -- -- <0.001 -- -- -- -- 0.310 0.914

NAT vs WC -- <0.001 -- <0.001 -- <0.001 0.905 0.062 0.250 0.019 0.176 0.509

NAT vs WF -- <0.001 -- 0.003 -- <0.001 0.029 0.120 0.041 0.010 0.144 0.268

WC vs WF -- <0.001 -- 0.521 -- 0.364 0.039 0.736 0.337 0.704 0.910 0.649

129

Table 3.10. Partial model of probabilities of differences between years in total shoot biomass, root, R:S, concentration N in shoot mass, concentration N in root mass, shoot mass N, and root mass N of native and agronomic communities at southern Alberta sites in 1995 and 1997.

Biomass Shoot Mass Root Mass R:S Shoot % N Root % N Shoot N Root N Total N

Stipa-Bouteloua --------------------------------------------------------------------------------------Probabilities-----------------------------------------------------------------------------------------------------------

Treatment

Native 0.012 0.903 0.038 0.013 0.281 0.672 0.943 0.039 0.043

Crested Wheatgrass 0.645 <0.001 0.086 0.053 <0.001 0.425 <0.001 0.183 0.936

Russian Wildrye 0.420 0.753 0.246 0.166 <0.001 0.322 0.015 0.517 0.941

Wheat Continuous 0.008 <0.001 0.250 0.362 <0.001 0.042 <0.001 0.099 0.476

Wheat Fallow <0.001 <0.001 0.177 0.825 <0.001 0.744 <0.001 0.130 <0.001

Stipa-Bouteloua-Agropyron --------------------------------------------------------------------------------------Probabilities-----------------------------------------------------------------------------------------------------------

Treatment

Native <0.001 0.034 <0.001 <0.001 0.412 0.001 0.008 <0.001 <0.001

Crested Wheatgrass 0.223 <0.001 <0.001 0.040 0.729 <0.001 0.008 <0.001 <0.001

Russian Wildrye <0.001 0.274 <0.001 <0.001 0.399 <0.001 0.232 <0.001 <0.001

Wheat Continuous 0.028 <0.001 0.029 0.352 0.892 <0.001 <0.001 0.002 0.205

Wheat Fallow <0.001 <0.001 0.308 0.625 0.010 <0.001 <0.001 0.096 0.271

Festuca-Danthonia ---------------------------------------------------------------------------------------Probabilities----------------------------------------------------------------------------------------------------------

Treatment

Native 0.019 0.602 0.022 0.491 <0.001 0.114 0.409 0.014 0.017

Smooth Brome 0.301 <0.001 0.035 0.292 <0.001 0.388 <0.001 0.228 0.746

Orchardgrass 0.500 0.101 0.330 0.001 0.065 0.114 0.021 0.364 0.509

Wheat Continuous 0.405 <0.001 0.845 0.348 0.851 0.989 <0.001 0.903 0.777

Wheat Fallow 0.004 <0.001 0.442 0.919 0.005 0.042 <0.001 0.728 0.145

130

APPENDIX B

NITROGEN PARTITIONING TABLES IN CHAPTER 4

131

Table 4.1. Monthly precipitation (mm) over the growing season from 1995 to 1997 atthree sites in southern Alberta.


Stipa-Bouteloua

1995 17 37 41 130 56 50 48 379 148

1996 32 13 64 80 33 4 51 277 109

1997 28 15 84 65 11 23 20 246 96

Ave. 2 22 28 41 64 34 39 27 255 100


1995 10 38 106 138 66 44 19 421 137

1996 21 22 54 18 5 70 6 196 64

1997 33 14 96 101 32 33 10 319 104

Ave. 2 24 31 55 74 42 42 40 308 100

Festuca-Danthonia 3

1995 6 23 72 84 69 39 63 356 83

1996 45 24 72 49 7 4 54 255 60

1997 15 21 138 73 28 77 35 387 91

Ave.3 24 14 99 113 74 69 34 427 100

1 Percent of 50-year average.2 50-year averages - Agriculture and Agrifood Canada.3 Measured at Claresholm.

132

Table 4.2. Total model for total soil nitrogen, mineralizable nitrogen, C:N in soil,ammonium (NH4

+), nitrate (NO3-), light fraction (LF), and total light

fraction nitrogen at three southern Alberta sites in 1995 and 1997.

Mineralizable N (mg kg-1) NH4+ (mg kg-1) NO3

- (mg kg-1) LF (mg g-1) Total LF N (mg kg-1)

Source ----------------------------------------------------------------------Probabilities---------------------------------------------------------------------

Year (Y) 0.006 <0.001 0.360 <0.001 <0.001

Site (S) <0.001 <0.001 0.013 <0.001 <0.001

Treatment (T) 0.163 0.318 <0.001 <0.001 <0.001

S x Y 0.012 <0.001 0.005 <0.001 <0.001

T x Y 0.248 0.468 <0.001 <0.001 <0.001

T x S 0.674 0.513 0.282 <0.049 <0.031

S x Y x T 0.891 0.505 0.041 <0.001 <0.001

Site ---------------------------------------------------------------------------Means------------------------------------------------------------------------

Stipa-Bouteloua

Native 52.580 8.400 1.990 26.340 345.000

Perennial Grass1 41.300 7.700 2.500 15.850 205.000

Wheat2 40.980 8.270 5.500 12.780 172.000

SE 9.680 2.040 0.900 6.740 140.000


Native 31.950 7.030 2.650 40.620 670.000

Perennial Grass1 27.260 6.690 2.390 21.100 310.000

Wheat2 35.730 6.800 6.650 15.390 240.000

SE 9.680 2.040 0.900 6.740 140.000

Festuca-Danthonia

Native 149.420 17.030 2.860 74.790 1410.000

Perennial Grass1 131.390 16.390 4.240 40.070 690.000

Wheat2 147.100 20.620 9.220 25.680 430.000

SE 9.680 2.040 0.900 5.830 140.000

133

Total N (mg g-1)

Mineralizable N (mg kg-1)NH4

+

(mg kg-1)NO3

-

(mg kg-1)SoilC:N

LF Total LF N(mg kg-1)

LF C:N

Source ---------------------------------------------------------------Probabilities--------------------------------------------------------------------------Year (Y) 0.113 0.006 <0.001 0.360 0.016 <0.001 <0.001 <0.001Site (S) <0.001 <0.001 <0.001 0.013 <0.001 <0.001 <0.001 <0.001Treatment (T) 0.325 0.163 0.318 <0.001 0.003 <0.001 <0.001 <0.001S x Y 0.138 0.012 <0.001 0.005 <0.001 <0.001 <0.001 <0.001T x Y 0.011 0.248 0.468 <0.001 0.034 <0.001 <0.001 0.304T x S 0.261 0.674 0.513 0.282 0.753 <0.049 <0.031 0.080S x Y x T 0.037 0.891 0.505 0.041 0.087 <0.001 <0.001 0.025Site ----------------------------------------------------------------Means--------------------------------------------------------------------------------Stipa-BoutelouaNative 1.570 52.580 8.400 1.990 9.790 26.340 345.000 18.410Perennial Grass1 1.510 41.300 7.700 2.500 9.500 15.850 205.000 18.370Wheat2 1.570 40.980 8.270 5.500 9.390 12.780 172.000 17.550SE 0.310 9.680 2.040 0.900 0.130 6.740 140.000 0.460

134

Table 4.2 (Continued).

Total N (mg g-1)

MineralizableN

(mg kg-1)NH4

+

(mg kg-1)NO3

-

(mg kg-1)SoilC:N

LF Total LF N(mg kg-1)

LF C:N

Site -------------------------------------------------------------------------------Means-----------------------------------------------------------------

Stipa-Agropyron-BoutelouaNative 2.870 31.950 7.030 2.650 9.860 40.620 670.000 15.690Perennial Grass1 2.760 27.260 6.690 2.390 9.720 21.100 310.000 16.010Wheat2 2.680 35.730 6.800 6.650 9.470 15.390 240.000 14.650SE 0.310 9.680 2.040 0.900 0.130 6.740 140.000 0.460Festuca-DanthoniaNative 6.720 149.420 17.030 2.860 11.880 74.790 1410.000 17.430Perennial Grass3 6.540 131.390 16.390 4.240 11.790 40.070 690.000 17.900Wheat2 7.310 147.100 20.620 9.220 11.670 25.680 430.000 16.360SE 0.310 9.680 2.040 0.900 0.130 5.830 140.000 0.4601 Results a combination of crested wheatgrass and Russian wildrye.2 Results a combination of fallow and continuously cropped wheat.3 Results a combination of smooth bromegrass and orchardgrass.

135

Table 4.3. Partial model by site for total soil nitrogen, mineralizable nitrogen , C:N in soil, Ammonium (NH4+), Nitrate (NO3

-) light fraction (LF), total light fraction nitrogen and C:N of the light fraction at three southern Alberta sites in 1995 and 1997.

Total N(mg g-1)

MineralizableN

(mg kg-1)SoilC:N

NH4+

(mg kg-1)NO3

-

(mg kg-1)LF

(mg kg-1)Total LF N(mg kg-1)

LFC:N

Site ------------------------------------------------------------------------Probabilities-------------------------------------------------------------

Stipa-BoutelouaTreatment (T) 0.636 0.505 0.220 0.460 <0.001 <0.001 <0.001 0.277Year (Y) 0.671 0.510 <0.001 <0.001 0.100 <0.001 0.003 <0.001T x Y 0.098 0.041 0.068 0.687 0.964 0.006 0.079 0.557Stipa-Bouteloua-AgropyronTreatment (T) 0.366 0.030 0.037 0.938 <0.001 <0.001 <0.001 <0.001Year (Y) 0.082 0.001 <0.001 <0.001 0.004 0.540 0.473 0.696T x Y 0.094 0.896 0.064 0.476 <0.001 0.177 0.376 0.068Festuca-DanthoniaTreatment (T) 0.285 0.270 0.171 0.393 0.002 0.002 0.005 0.036Year (Y) 0.018 0.006 <0.001 <0.001 0.711 <0.001 <0.001 0.010T x Y 0.036 0.281 0.404 0.056 0.003 0.003 0.005 0.021

136

Table 4.4. Effects of agronomic and native communities on mineralizable N, ammonium (NH4+), and nitrate (N03

-) in upper 15 cm of soil1 and light fraction, light fraction N, and C:N in upper 7.5 cm in a Stipa-Bouteloua site in southern Alberta in 1995 and 1997.

Mineralizable N(mg kg-1)

NH4+

(mg kg-1)NO3

-

(mg kg-1)LF

(mg kg-1)LF N

(mg kg-1)LF

C:N1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment ------------------------------------------------------------------------------Means-----------------------------------------------------------------

Native 48.300 62.000 10.000 6.900 2.900 1.500 16.300 38.400 244.000 471.000 19.200 17.600Crested Wheatgrass 49.900 38.700 11.000 7.200 3.600 1.400 13.600 18.100 193.000 215.000 19.700 17.800Russian Wildrye 41.800 35.200 9.700 4.100 3.100 1.700 10.500 20.300 160.000 240.000 19.500 17.100Wheat Continuous 41.500 41.300 10.600 7.500 5.100 4.900 9.600 16.200 135.000 206.000 19.400 16.400Wheat Fallow 46.100 35.000 10.200 4.900 5.300 6.600 10.700 14.700 156.000 190.000 18.500 15.900SE2 8.000 6.600 1.200 1.400 0.740 0.520 1.500 2.400 26.000 35.000 0.700 0.000

Contrast ------------------------------------------------------------------Probabilities3---------------------------------------------------------------------

Native vs PerennialGrass 0.800 0.012 0.632 0.514 0.626 0.877 0.037 <0.001 0.052 <0.001 0.640 0.806

Native vs Wheat 0.634 0.013 0.626 0.711 0.020 <0.001 0.010 <0.001 0.010 <0.001 0.796 0.014Perennial Grass vs

Wheat 0.774 0.863 0.991 0.719 0.015 <0.001 0.169 0.169 0.202 0.169 0.337 0.010

1 Soil samples contain root biomass. 2 Standard error of the sample population. 3 Probabilities of planned contrasts.

137

Table 4.5. Effects of agronomic and native communities on mineralizable N, ammonium (NH4+) and nitrate (N03

-) in upper 15 cm of soil1 and light fraction, light fraction N, and C:N in upper 7.5 cm in a Stipa-Agropyron-Bouteloua site in southern Alberta in 1995 and 1997.


NH4+

(mg kg-1)NO3

-

(mg kg-1)LF

(mg kg-1)LF N

(mg kg-1)LF

C:N

1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment -------------------------------------------------------------------------------------------------Means----------------------------------------

Native 31.200 29.100 7.800 6.000 2.800 2.500 32.800 44.000 570.000 702.000 15.400 16.100

Crested Wheatgrass 30.900 21.200 7.200 6.400 2.200 2.600 19.200 21.800 299.000 309.000 15.500 16.500

Russian Wildrye 33.400 23.500 7.400 5.800 2.100 2.600 20.200 23.200 329.000 320.000 15.800 16.200

Wheat Continuous 38.000 31.900 7.400 5.900 3.000 11.900 16.100 14.900 260.000 219.000 15.500 14.200

Wheat Fallow 40.900 31.800 8.300 5.700 4.300 7.600 18.300 12.600 314.000 194.000 14.900 14.100

SE2 2.800 2.700 0.500 0.600 0.400 0.800 2.900 3.100 48.000 51.000 0.340 0.410

Contrast --------------------------------------------------------------------------------------------Probabilities3-------------------------------------

Native vs Perennial Grass 0.778 0.066 0.464 0.865 0.202 0.930 0.003 <0.001 0.001 <0.001 0.462 0.662

Native vs Wheat 0.036 0.406 0.864 0.788 0.110 <0.001 0.001 <0.001 <0.001 <0.001 0.670 0.002

Perennial Grass vs Wheat 0.015 0.004 0.242 0.593 0.002 <0.001 0.344 0.015 0.537 0.058 0.139 <0.001

1 Soil samples contain root biomass.

2 Standard error of the sample population. 3 Probabilities of planned contrasts.

138

138

Table 4.6. Effects of agronomic and native communities on mineralizable N, ammonium (NH4+), nitrate (N03

-) in upper 15 cm of soil1 and light fraction, light fraction N and C:N ration in upper 7.5 cm in a Festuca Danthonia site in southern Alberta in 1995 and 1997.


NH4+

(mg kg-1)NO3

-

(mg kg-1)LF

(mg kg-1)LF N

(mg kg-1)LF

C:N

1995 1997 1995 1997 1995 1997 1995 1997 1995 1997 1995 1997

Treatment ------------------------------------------------------------------------------------------------Means---------------------------------------

Native 156.400 134.000 24.400 10.600 2.900 3.100 26.400 123.200 466.000 2348.00 19.100 15.800

Smooth Bromegrass 120.900 99.800 21.600 11.700 7.200 2.200 13.000 43.000 216.000 706.00 17.900 18.900

Orchardgrass 183.500 121.400 22.600 10.900 5.400 2.200 34.600 69.700 590.000 1234.00 18.600 16.200

Wheat Continuous 139.600 131.600 20.300 12.800 6.700 7.800 16.200 41.800 272.000 795.00 17.700 15.400

Wheat Fallow 187.700 118.200 32.800 9.900 7.000 12.500 20.300 25.100 372.000 409.00 16.000 16.300

SE2 19.500 16.600 3.300 2.200 1.100 1.700 5.300 13.500 108.000 282.00 0.700 0.500

Contrast --------------------------------------------------------------------------------------------Probabilities3----------------------------------

Native vs Perennial Grass 0.862 0.251 0.580 0.701 0.016 0.655 0.700 0.002 0.646 0.002 0.339 0.010

Native vs Wheat 0.775 0.646 0.613 0.890 0.008 0.004 0.258 <0.001 0.318 <0.001 0.025 0.921

Perennial Grass vs Wheat 0.586 0.349 0.223 0.745 0.577 <0.001 0.350 0.136 0.492 0.239 0.077 0.0041 Soil samples contain root biomass 2 Standard error of the sample population 3 Probabilities of planned contrasts

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