Soil Fertility Dynamics

T. Scott Murrell

Director, Northcentral U.S.

National Alliance of Independent Crop Consultants,

2013 Annual Meeting, Jacksonville, FL. 22-26 Jan. 2013.

IPNI Nutrient Evaluation Efforts

• Soil Test Summaries

• Nutrient Use GIS

Median Bray P-1 equivalent

soil test levels, 2010

Change in median Bray P equivalent soil

test levels from 2005 to 2010

Soil test P distribution in 2010 compared to

2005 for the Corn Belt (12 states plus Ontario)

0%

5%

10%

15%

20%

25%

30%

Bray P1 Equivalent, ppm

Corn Belt P 2005 2.0 million samples2010 3.0 million samples

(2010) 22 28 (2005)

Median

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1987 P2O5 Balance

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1992 P2O5 Balance

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1997 P2O5 Balance

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2002 P2O5 Balance

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2007 P2O5 Balance

Expected changes in soil test levels

based upon nutrient budgets

Ch

an

ge

in

so

il t

es

t le

ve

l

~ 0

+

-

Application > removal

Application < removal

Application ≈ removal

Annual change in median soil P level for 12 Corn Belt

states as related to state P balance, 2005-2009

*NuGIS is a GIS nutrient balance model (IPNI, 2010).

y = 0.0897x - 0.063

r² = 0.62

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

-25 -20 -15 -10 -5 0 5

An

nu

al c

han

ge i

n m

edia

n P

, p

pm

NuGIS balance*, lb P2O5/A/yr

WI

IL

MI

IA

MN

SD

KS

OH

IN

NE

KY

MO

11 lb P2O5 / ppm

Median soil test K levels in 2010

Change in median soil K level from 2005 to 2010

Soil test K frequency distribution in 2001,

2005 and 2010

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1987 K2O Balance

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1992 K2O Balance

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1997 K2O Balance

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2002 K2O Balance

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2007 K2O Balance

Soil Test Potassium:

Difficulties with Identifying Trends

• Changes that occur are not consistently predictable

• What could be contributing to this variability?

Long-term crop removal and soil test P trends

0

1

2

3

4

5

6

7

8

9

10

0

100

200

300

400

500

0 2 4 6 8 10 12

Soil

P d

ecre

ase (

ppm

)

P r

em

oval (lb P

2O

5/a

cre

)

Years of corn/soybean rotation

P Removal Soil P decrease

Villavicencio and Mallarino, 2011. Personal communication

43 lb P2O5 / ppm

Long-term crop removal and soil test K trends

Villavicencio and Mallarino, 2011. Personal communication

0

10

20

30

40

50

60

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12 14 16

Soil

K d

ecre

ase (

ppm

)

K r

em

oval (lb K

2O

/acre

)

Years of corn/soybean rotation

K Removal Soil K Decrease

12 lb K2O / ppm

Contributors to soil test K variability:

Sampling variability

Short-range variability of soil test K:

Across and down

Nutrient stratification

Banding 2 yr. ago

Banding 4 yr. ago

Banding this year

Depth control:

Important in reduced tillage systems

440 580

330 440

160

330

440

37 in. 37 in.

0

10

Dep

th (

in.)

160 6

Robbins and Voss, 1991 (IA)

8 in.

160 – 580 ppm

4 in.

330 – 580 ppm

No-till field with 10-yr history

Tama silt loam

Core number: Impact on variability

Soil test P category upper limit (ppm)

Fre

qu

en

cy (

50

to

tal)

0 2

17 20

7 3

1 0

5

10

15

20

25

30

35

40

5 cores per sample

0 0

8

34

8

0 0 0

5

10

15

20

25

30

35

40

10 20 30 40 50 60 70

20 cores per sample

True average

Contributors to soil test K variability:

Sampling frequency

Sampling frequency: Affects ability to detect trends

Crop year

So

il t

es

t le

ve

l

1 2 3 4 5 6 7 8

Increasing or decreasing?

Sampled every 4 years Sampled every 2 years Sampled every 1 year

Concept of a monitoring strip

Area where intensive

measurements are taken each

season

• Soil tests

• Plant tissue tests

• Nutrient deficiency

symptoms

• Grain nutrient content

• Diseases

• Insects

• Management practices

• etc.

Visual symptoms of K deficiency are a

useful diagnostic tool

170

0.0

0.5

1.0

1.5

2.0

0 50 100 150 200

K v

isu

al d

efic

ien

cy s

ymp

tom

ind

ex

Soil test K (ppm)

Deficiency Symptom Index:

0 = None

1 = Moderate

2 = Severe

Wittry and Mallarino, Iowa State University

Example of K deficiency symptoms:

soybean

Contributors to soil test K variability:

Leaching of K from plant residue

Changes in corn stover K content after

physiological maturity

Oltmans and Mallarino. 2011. Personal communication.

0

20

40

60

80

100

120

140

160

-50 0 50 100 150 200 250

Corn

sto

ver

K c

onte

nt (lb

K2O

/acre

)

Days since physiological maturity

harvest

Changes in soybean tissue K content

after physiological maturity

Oltmans and Mallarino. 2011. Personal communication.

0

20

40

60

80

100

120

140

160

-50 0 50 100 150 200 250

Soybean tis

sue K

conte

nt (lb

K2O

/acre

)

Days since physiological maturity

harvest

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Water, inches

Pe

rcen

t o

f in

itia

l K

rem

ain

ing

Non-irrigated

Irrigated by overland flow

(2 in. every 7-21 days)

Schomberg, H.H. and J.L. Steiner. 1999. Soil Sci. Soc. Am. J. 63:607-613

Amount of water affecting K leaching

from residue

Contributors to soil test K variability:

Soil moisture

Potassium fixation Dehydrated K ion

Hydrated K ion

Clay mineral layer

Interlayer

positions

Havlin et al., 1999

Planar positions

Edge positions

Wetting/drying cycles impact variability

Sample Treatment Fixed K Exchangeable K

--------- meq/100g ----------

Drummer (Dekalb)

Dry 72.8 29.6

Wet 66.6 38.6

Drummer (Urbana)

Dry 71.6 33.7

Wet 65.7 39.6

Cisne (Brownstone)

Dry 43.9 30.9

Wet 39.2 42.9

Stucki, 1996 (IL)

Seasonal variation in soil test K

0

5

10

15

20

25

30

35

40

45

50

60

70

80

90

100

110

120

130

140

150

160

170

J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A

Soil

mois

ture

(%

)

Soil

test

K (

ppm

)

Month of the year

Soil test K

Soil moisture

1994 1997 1996 1995

Ebelhar et al. 1997. Personal communication. Soil test values are ammonium acetate extractable.

How the scientific community is

responding to variability in soil test K

Two primary efforts have been underway to address K

variability:

• Conduct new crop response trials

• Re-examine the effect of drying soils prior to analysis

Scientific response to

soil test K variability:

Updated crop response trials

Changes in soil test K critical levels:

Categories used previously – Iowa, U.S.

Mallarino, A.P. 2003.

40

50

60

70

80

90

100

110

0 50 100 150 200 250 300 350

Co

rn g

rain

rel

ativ

e yi

eld

(%

)

Soil test K (ppm)

Very

low

Low

Optim

um

Hig

h

Very

hig

h

Changes in soil test K critical levels:

Categories used previously – Iowa, U.S.

Mallarino, A.P. 2003.

40

50

60

70

80

90

100

110

0 50 100 150 200 250 300 350

Co

rn g

rain

rel

ativ

e yi

eld

(%

)

Soil test K (ppm)

Many other soils

Canisteo, Colo, Ely, Nicollet, Tama, Webster

Very

low

Low

Optim

um

Hig

h

Very

hig

h

Changes in soil test K critical levels:

Categories currently used – Iowa, U.S.

Mallarino, A.P. 2003.

40

50

60

70

80

90

100

110

0 50 100 150 200 250 300 350

Co

rn g

rain

rel

ativ

e yi

eld

(%

)

Soil test K (ppm)

Many other soils

Canisteo, Colo, Ely, Nicollet, Tama, Webster

Very

low

Low

Optim

um

Hig

h

Very

hig

h

Scientific response to

soil test K variability:

Re-examining the effect of drying soils

prior to analysis

Monitoring soil test K over time:

Effects of drying the soil sample

Field moist Air-dried

Mallarino, A.P. Personal communication. Soil test values are ammonium acetate extractable.

K applications

discontinued

0

50

100

150

200

250

0 10 20 30 40

Soil

test

K (

ppm

)

Years of corn/soybean rotation

0 lb K2O/acre

108 lb K2O/acre

Effect of sample drying on soil test K

y = 161.23x-0.543 R² = 0.9527

y = 84.336x-0.278 R² = 0.88

0

20

40

60

80

100

120

0 5 10 15 20 25 30

Soil

test

K (

pp

m)

Soil moisture (%)

Harpster silty clay loam

Clarion loam

Luebs, R.E. et al. 1956. Soil Sci. Soc. Am. Proc 20:45-50. Note: curve fitting and statistics not performed by the authors.

Initial soil test K levels affect changes as

soils are dried

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30

Soil

test

K (

pp

m)

Soil moisture (%)

Bedford: no K added

Bedford: K enriched

Dowdy, R.J. and T.B. Hutcheson, Jr. 1963. Soil Sci. Soc. Am. Proc. 27:31-34.

Keeping samples moist may improve the

relationship of soil test K to yield response

Barbagelata and Mallarino. 2005. Personal communication.

60

70

80

90

100

110

0 100 200 300 400 500

Co

rn r

elat

ive

yiel

d (

%)

Soil test K (ppm)

Clay loam

Loam

Silty clay loam

Dried

Keeping samples moist may improve the

relationship of soil test K to yield response

Barbagelata and Mallarino. 2005. Personal communication.

60

70

80

90

100

110

-50 50 150 250 350 450

Co

rn r

elat

ive

yiel

d (

%)

Soil test K (ppm)

Clay loam

Loam

Silty clay loam

Moist

Summary

• Soil test P levels are declining in the Midwest, and these declines can be explained by mass balance

• Soil test K levels are declining in many states in the Midwest, but declines are not explained by mass balance perhaps because of high variability

• Causes of soil test K variability:

– Sampling variability

– Sampling frequency

– Leaching of K from crop residues

– Soil moisture

– Drying of soil samples prior to analysis

• Scientific response:

– Update crop response data

– Investigate drying of soils prior to analysis