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Organic Matter BudgetOrganic Matter Budget
Marianne SarrantonioMarianne Sarrantonio
University of MaineUniversity of Maine
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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Chemical Structure of PlantChemical Structure of Plant CompoundsCompounds
LIGNIN
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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
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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.
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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
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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
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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
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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)
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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
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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)
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EXAMPLE 1 WORKSHEET CALCULATIONS
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
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Rotational Accumulation Exercise WorksheetExample 1
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)
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EXAMPLE 2 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: 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
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EXAMPLE 2 WORKSHEET CALCULATIONS
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
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Rotational Accumulation Exercise WorksheetExample 2
Start of Rotation:
Organic Matter (SOM0) ___50,000__ Balance
Year 1Subtract SOM0 x k1 -__1,500___ _48,500__
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
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EXAMPLE 2A 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: Silage corn @ 1000 lb/ac residue; k2= 75% (0.75)
COVER CROP (planted previous fall): Hairy vetch @ 3000 lb/ac
k2 = 80% (0.80)
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Rotational Accumulation Exercise WorksheetExample 2A
Start of Rotation:
Organic Matter (SOM0) _ 50,000___ Balance
Year 1Subtract SOM0 x k1 -__1,500___ _48,500__
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
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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
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Rotational Accumulation Exercise WorksheetExample 2B
Organic Matter (SOM0) ___50,000__ Balance
Year 1Subtract SOM0 x k1 -__1,950___ _48,050__
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
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EXAMPLE 2B WORKSHEET CALCULATIONSFor FOUR YEAR ROTATION
YEAR 2
TILLAGE: Conventional, once in the late spring
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
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Rotational Accumulation Exercise WorksheetExample 2B
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
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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
EXAMPLE 2B WORKSHEET CALCULATIONSFor FOUR YEAR ROTATION
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Rotational Accumulation Exercise WorksheetExample 2B
Organic Matter (SOM2) ___48,893__ Balance
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
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EXAMPLE 2B WORKSHEET CALCULATIONSFor FOUR YEAR ROTATION
YEAR 4
TILLAGE: Conventional, once in the late spring
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
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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
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WAYS TO INCREASE OMWAYS TO INCREASE OM
REDUCE KREDUCE K22
REDUCE KREDUCE K11
INCREASE NAINCREASE NA
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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!)
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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
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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
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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
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….and in all things, it is most important to keep your sense of humus.
- Anon