Organic Matter Budget Marianne Sarrantonio University of Maine.

Organic Matter BudgetOrganic Matter Budget

Marianne SarrantonioMarianne Sarrantonio

University of MaineUniversity of Maine

Now, here, you see, it takes all the running you can do to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that.

-Lewis Carroll

In Through the Looking Glass

Benefits of Soil Organic Matter

Increases soil aggregation

Increases soil water holding capacity (WHC)

Improves water infiltration rates

Increases cation exchange capacity (CEC)

Improves nutrient cycling

Helps solubilize some mineral nutrients

Serves as habitat / food source for soil life

Dark color helps warm soil

Smells good

B S

B S

B S

B S

FallowCover crop

BS

BroccoliSquashConv.

Fall CC

2-Yr CCAlt. Yr CC

“LONG-TERM” VEGETABLE / COVER CROP TRIAL

University of Maine

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Bul

k D

ens

ity

(Mg

m-2

)

ab b

b

0

5

10

15

20

25

30

35

Conv Fall CC 2-Yr CC Alt. Yr CC

Wat

er

hol

ding

capa

city

(%

)

System

ab

bc c

LONG-TERM VEGETABLE / COVER CROP TRIAL

LONG-TERM VEGETABLE COVER CROP TRIAL

%Water Stable Aggregates 2005

0

5

10

15

20

25

30

35

40

C F 2YR ALTYR

2-4 mm

.5- 2mm

.05- .5 mm

Pools of Soil Organic Matter

Fresh organic material, Partially decomposed mat’l, Humus

The living….the dead… the very dead (Magdoff, 2000)

Active fraction Passive fraction (Brady and Weil, 2001)

Labile fraction Recalcitrant fraction

Litter, Mic biomass, Light fraction, Stable fraction, Old SOM

(Paul and Juma, 1981)

LITTER:

Recently killed organic residues not yet incorporated

0-20% of SOM

ACTIVE FRACTION:

Microbial Biomass

Organic residues in various stages of decomposition

Non-humic substances

2-30% of SOM (Stevenson, 1994, Janzen et al. 1992)

STABLE FRACTION:

Humic substances

70-96% of SOM

Plant Litter Composition

Simple sugars

Starches

Proteins and amino acids

Hemicellulose

Cellulose

Fats, waxes, oils

Lignin and polyphenolics

Ease o

f Deco

mp

ositio

n

Chemical Structure of Plant Chemical Structure of Plant CompoundsCompounds

H-C-O

H-C-OH

HO-C-H

H-C-OH

H-C-OH

C-H2OH

GLUCOSE AMINO ACID

H

R - C – NH2

COOH

Chemical Structure of PlantChemical Structure of Plant CompoundsCompounds

LIGNIN

Factors Affecting Decomposition of Factors Affecting Decomposition of Organic MatterOrganic Matter

Chemical composition of litterChemical composition of litter Tillage intensity and frequencyTillage intensity and frequency Size of residue piecesSize of residue pieces Soil-litter contact/depth of placementSoil-litter contact/depth of placement Soil temperatureSoil temperature Soil moisture/ soil aerationSoil moisture/ soil aeration Soil pHSoil pH Soil textureSoil texture Microbial biomass size and activityMicrobial biomass size and activity

Soil Organic Matter at the end of a year equals the SOM at the end of last year, plus the current year’s additions of organic residues, minus the losses of each fraction through decomposition during the current year.

SOM1 = (SOM0 – SOM0*k1) + (NA – NA*k2)

Where SOM1 is the soil organic matter at the end of current year

SOM0 is the coil organic matter at the end of last year

NA = new additions of organic residue

k1 = the decomposition rate of SOM0

k2 = the decomposition rate of NA

FACTORS AFFECTING KFACTORS AFFECTING K11

Baseline for silt loam in temperate climate Baseline for silt loam in temperate climate = approx. 2%/yr= approx. 2%/yr

Conventional tillage can increase by 50%Conventional tillage can increase by 50% Additional tillage/ yr can increase by 30%Additional tillage/ yr can increase by 30% Drought decreasesDrought decreases Hot weather increasesHot weather increases Light soils increases/ heavy decreasesLight soils increases/ heavy decreases Wet soils (> 60% WFPS) decreasesWet soils (> 60% WFPS) decreases Previous losses of active fraction Previous losses of active fraction

decreasesdecreases Large additions to active fraction increasesLarge additions to active fraction increases

FACTORS AFFECTING KFACTORS AFFECTING K22

C:N ratioC:N ratio Carbon profile (i.e. % lignin, Carbon profile (i.e. % lignin,

cellulose, etc.)cellulose, etc.) Age / maturityAge / maturity

Rotational Accumulation Exercise Worksheet

Start of Rotation:

Organic Matter (SOM0) __________ Balance

Year 1Subtract SOM0 x k1 -__________ _________

Add NA- (NA x k2) +__________ _________

Add NA- (NA x k2)(2nd amendment ) +__________ _________

Organic Matter at end of Year 1 (SOM1) __________(carry)

EXAMPLE 1 WORKSHEET CALCULATIONS

SOIL: sandy loam with 2.5% organic matter at start of rotation

CLIMATE: Northeast (cool, humid)

TILLAGE: Conventional, once in the late spring

K1 : 3%

CROP: Grain corn

ASSUME:

1 acre of soil to 6” depth weighs approx. 2,000,000 lb (@1.3 kg m3)

Therefore:

Organic matter at start of rotation (SOM0) = 2,000,000lb/ac x 0.025

= 50,000 lb/ac

SOM0 x k1 = 50,000 lb/ac x .03 = 1500 lb/ac

Rotational Accumulation Exercise WorksheetExample 1

Start of Rotation:

Organic Matter (SOM0) _50,000____ Balance

Year 1Subtract SOM0 x k1 -__1,500____ __48,500_

Add NA- (NA x k2) +__________ _________

Add NA- (NA x k2)(2nd amendment ) +__________ _________

Organic Matter at end of Year 1 (SOM1) __________(carry)


ASSUME: 5000 lb/ac corn residue remains in the fall

K2 corn grain residue: 70% (0.70)

THEREFORE:

NA – (NA x k2) = 5,000lb/ac - (5000 lb/ac x 0.70)

= 5,000 lb/ac – 3,500 lb/ac

= 1,500 lb/ac


Start of Rotation:

Organic Matter (SOM0) lb/ac __50,000___ Balance

Year 1Subtract SOM0 x k1 -__1,500___ _48,500__

Add NA- (NA x k2) +__1,500___ _50,000__

Add NA- (NA x k2)(2nd amendment ) +____0____ _50,000__

Organic Matter at end of Year 1 (SOM1) __50,000___(carry)





K1 : 3%

CROP: Silage corn (k2 = 0.75)

Organic matter at start of rotation (SOM0) = 2,000,000lb/ac x 0.025

= 50,000 lb/ac

SOM0 x k1 = 50,000 lb/ac x .03 = 1500 lb/ac


ASSUME: 1000 lb/ac corn residue remains in the fall

K2 silage residue: 75% (0.75)

THEREFORE:

NA – (NA x k2) = 1,000lb/ac - (1,000 lb/ac x 0.75)

= 1,000 lb/ac – 750 lb/ac

= 250 lb/ac


Start of Rotation:

Organic Matter (SOM0) ___50,000__ Balance


Add NA- (NA x k2) silage +__250____ _48, 750__

Add NA- (NA x k2)(2nd amendment ) +____0____ _ 48,750__

Organic Matter at end of Year 1 (SOM1) __48,750__(carry)

LOSS: 1,250 lb/ac or 2.5% of SOM0

EXAMPLE 2A WORKSHEET CALCULATIONS




K1 : 3%

CROP: Silage corn @ 1000 lb/ac residue; k2= 75% (0.75)

COVER CROP (planted previous fall): Hairy vetch @ 3000 lb/ac

k2 = 80% (0.80)

Rotational Accumulation Exercise WorksheetExample 2A

Start of Rotation:

Organic Matter (SOM0) _ 50,000___ Balance


Add NA- (NA x k2) +__250____ _48, 750__

Add NA- (NA x k2)(2nd amendment ) +__600____ _ 49,350__

Organic Matter at end of Year 1 (SOM1) _49,350__(carry)

LOSS: 650 lb/ac or 1.3% of SOM0

EXAMPLE 2B WORKSHEET CALCULATIONS

For FOUR YEAR ROTATION

YEAR 1

TILLAGE: Conventional, once in the late spring, once in fall

K1 : 3.9 % (increase by 30% for additional tillage)

CROP: Silage corn @ 1000 lb/ac residue; k2 = 0.75

COVER CROP (planted previous fall): Hairy vetch @ 3000 lb/ac; k2 = 80% (0.80)

COVER CROP (Fall seeding) Cereal rye

Rotational Accumulation Exercise WorksheetExample 2B



Add NA- (NA x k2) silage +__250____ _48, 300__

Add NA- (NA x k2)(2nd amendment ) +__600____ _ 49,900__Hairy vetch

Organic Matter at end of Year 1 (SOM1) _48,900__(carry)

LOSS: 1100 lb/ac or 2.2% of SOM0

EXAMPLE 2B WORKSHEET CALCULATIONSFor FOUR YEAR ROTATION

YEAR 2


K1 : 3.0 %

CROP: Soybeans @ 2000 lb/ac residue; k2 = 80% (0.80)

COVER CROP (planted previous fall): Cereal rye @ 6000 lb/ack2 = 75% (0.75)

COVER CROP (Fall seeding) none


Organic Matter (SOM1) __48,900___ Balance

Year 2Subtract SOM1 x k1 -__1,907 ___ __46,993_

Add NA- (NA x k2) soy +__ 400____ __47,393_

Add NA- (NA x k2)(2nd amendment ) +__1,500___ __48,893_Cereal rye

Organic Matter at end of Year 2 (SOM2) __48,896__(carry)

CUMULATIVE LOSS: 1,104 lb/ac or 2.2% of SOM0

YEAR 3

TILLAGE: Conventional, once in the late spring, once in fall

K1 : 3.9 % (increase by 30% for additional tillage)

CROP: Grain corn @ 5000 lb/ac residue; k2 = 70% (0.70)

COVER CROP (planted previous fall): none

COVER CROP (Fall seeding) Cereal rye




Year 3

Subtract SOM2 x k1 -_1,906____ __46,987_

Add NA- (NA x k2) grain corn +_1,500___ __48,487_

Add NA- (NA x k2)(2nd amendment ) +____0____ __48,487_

Organic Matter at end of Year 3 (SOM3) _48,487___(carry)

CUMULATIVE LOSS: 1,513 lb/ac or 3% of SOM0


YEAR 4


K1 : 3.0 %

CROP: Soybeans @ 2000 lb/ac residue, k2 = 0.80

COVER CROP (planted previous fall): Cereal rye, k2 = 0.75

COVER CROP (Fall overseeding) Hairy vetch

Rotational Accumulation Exercise Worksheet Example 2B

Organic Matter (SOM3) __48,847___ Balance

Year 4Subtract SOM3 x k1 -__1,455____ _47,032__

Add NA- (NA x k2) soy +___400____ _47,432__

Add NA- (NA x k2)(2nd amendment ) +__1,500____ _48,932__Cereal rye

Organic Matter at end of Year 4 (SOM4) __48, 932__(carry)

TOTAL LOSS AFTER 4 YEARS: 1,068 lb/ac or 2.14% of SOM0

TOTAL LOSS AFTER 8 YEARS: 2,115 lb/ac or 4.23% of SOM0

WAYS TO INCREASE OMWAYS TO INCREASE OM

REDUCE KREDUCE K22

REDUCE KREDUCE K11

INCREASE NAINCREASE NA

Best Ways to Reduce KBest Ways to Reduce K11

Reduce intensity of tillageReduce intensity of tillage Reduce frequency of tillageReduce frequency of tillage Reduce depth of tillageReduce depth of tillage Reduce area of tillage (e.g. zone till)Reduce area of tillage (e.g. zone till) Reduce mechanical cultivation (uh Reduce mechanical cultivation (uh

oh!)oh!)

BEST WAYS TO LOWER KBEST WAYS TO LOWER K22

Species / amendment choiceSpecies / amendment choice Allow covers to grow longerAllow covers to grow longer All other factors are already rolled All other factors are already rolled

into k1into k1

BEST WAYS TO INCREASE NABEST WAYS TO INCREASE NA

Plant cover crops in timely wayPlant cover crops in timely way Allow cover crops to grow longerAllow cover crops to grow longer Fill short niches with coversFill short niches with covers Full-year fallow with cover cropsFull-year fallow with cover crops Species choicesSpecies choices Supplement with manure and Supplement with manure and

compostcompost Use more small grains Use more small grains

TO DO LISTTO DO LIST

Include manure (kInclude manure (k22 = 0.20 – 0.50) = 0.20 – 0.50) and compost (kand compost (k22 = 0.10 – 0.30) = 0.10 – 0.30)

Develop as Excel worksheetDevelop as Excel worksheet Account for OM protection by clays Account for OM protection by clays

and aggregatesand aggregates Account for “small-grain effect”Account for “small-grain effect” Include more vegetable residuesInclude more vegetable residues Account for erosionAccount for erosion

….and in all things, it is most important to keep your sense of humus.

- Anon

Organic Matter Budget Marianne Sarrantonio University of Maine.

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