Organic Matter Budget Marianne Sarrantonio University 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

“LONG-TERM” VEGETABLE / COVER CROP TRIAL University of Maine

LONG-TERM VEGETABLE / COVER CROP TRIAL

LONG-TERM VEGETABLE COVER CROP TRIAL %Water Stable Aggregates 2005

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 of Decomposition

Chemical Structure of Plant Compounds H-C-O H-C-OH HO-C-H H-C-OH C-H2OH GLUCOSEAMINO ACID H R - C – NH2 COOH

Chemical Structure of Plant Compounds Chemical Structure of Plant Compounds LIGNIN

Factors Affecting Decomposition of Organic Matter Chemical composition of litter Chemical composition of litter Tillage intensity and frequency Tillage intensity and frequency Size of residue pieces Size of residue pieces Soil-litter contact/depth of placement Soil-litter contact/depth of placement Soil temperature Soil temperature Soil moisture/ soil aeration Soil moisture/ soil aeration Soil pH Soil pH Soil texture Soil texture Microbial biomass size and activity Microbial 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.

SOM 1 = (SOM 0 – SOM 0 *k 1 ) + (NA – NA*k 2 ) Where SOM 1 is the soil organic matter at the end of current year SOM 0 is the coil organic matter at the end of last year NA = new additions of organic residue k 1 = the decomposition rate of SOM 0 k 2 = the decomposition rate of NA

FACTORS AFFECTING K 1 Baseline for silt loam in temperate climate = approx. 2%/yr Baseline for silt loam in temperate climate = 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 decreases Drought decreases Hot weather increases Hot weather increases Light soils increases/ heavy decreases Light soils increases/ heavy decreases Wet soils (> 60% WFPS) decreases Wet soils (> 60% WFPS) decreases Previous losses of active fraction decreases Previous losses of active fraction decreases Large additions to active fraction increases Large additions to active fraction increases

FACTORS AFFECTING K 2 C:N ratio C:N ratio Carbon profile (i.e. % lignin, cellulose, etc.) Carbon profile (i.e. % lignin, cellulose, etc.) Age / maturity Age / maturity

Rotational Accumulation Exercise Worksheet Start of Rotation: Organic Matter (SOM 0 )__________Balance Year 1 Subtract SOM 0 x k 1 -___________________ Add NA- (NA x k 2 )+___________________ Add NA- (NA x k 2 )(2nd amendment )+___________________ Organic Matter at end of Year 1 (SOM 1 ) __________(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 K 1 : 3% CROP: Grain corn ASSUME: 1 acre of soil to 6” depth weighs approx. 2,000,000 lb kg m 3 ) Therefore: Organic matter at start of rotation (SOM 0 ) = 2,000,000lb/ac x = 50,000 lb/ac SOM 0 x k 1 = 50,000 lb/ac x.03 = 1500 lb/ac

Rotational Accumulation Exercise Worksheet Example 1 Start of Rotation: Organic Matter (SOM 0 )_50,000____Balance Year 1 Subtract SOM 0 x k 1 -__1,500______48,500_ Add NA- (NA x k 2 )+___________________ Add NA- (NA x k 2 )(2nd amendment )+___________________ Organic Matter at end of Year 1 (SOM 1 ) __________(carry)

EXAMPLE 1 WORKSHEET CALCULATIONS ASSUME: 5000 lb/ac corn residue remains in the fall K 2 corn grain residue: 70% (0.70) THEREFORE: NA – (NA x k 2 ) = 5,000lb/ac - (5000 lb/ac x 0.70) = 5,000 lb/ac – 3,500 lb/ac = 1,500 lb/ac

Rotational Accumulation Exercise Worksheet Example 1 Start of Rotation: Organic Matter (SOM 0 ) lb/ac__50,000___Balance Year 1 Subtract SOM 0 x k 1 -__1,500____48,500__ Add NA- (NA x k 2 )+__1,500____50,000__ Add NA- (NA x k 2 )(2nd amendment )+____0_____50,000__ Organic Matter at end of Year 1 (SOM 1 ) __50,000___(carry)

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 K 1 : 3% CROP: Silage corn (k 2 = 0.75) Organic matter at start of rotation (SOM 0 ) = 2,000,000lb/ac x = 50,000 lb/ac SOM 0 x k 1 = 50,000 lb/ac x.03 = 1500 lb/ac

EXAMPLE 2 WORKSHEET CALCULATIONS ASSUME: 1000 lb/ac corn residue remains in the fall K 2 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

Rotational Accumulation Exercise Worksheet Example 2 Start of Rotation: Organic Matter (SOM 0 )___50,000__Balance Year 1 Subtract SOM 0 x k 1 -__1,500____48,500__ Add NA- (NA x k 2 ) silage+__250_____48, 750__ Add NA- (NA x k 2 )(2nd amendment )+____0_____ 48,750__ Organic Matter at end of Year 1 (SOM 1 ) __48,750__(carry) LOSS: 1,250 lb/ac or 2.5% of SOM 0

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 K 1 : 3% CROP: Silage 1000 lb/ac residue; k 2 = 75% (0.75) COVER CROP (planted previous fall): Hairy 3000 lb/ac k 2 = 80% (0.80)

Rotational Accumulation Exercise Worksheet Example 2A Start of Rotation: Organic Matter (SOM 0 )_ 50,000___Balance Year 1 Subtract SOM 0 x k 1 -__1,500____48,500__ Add NA- (NA x k 2 )+__250_____48, 750__ Add NA- (NA x k 2 )(2nd amendment )+__600_____ 49,350__ Organic Matter at end of Year 1 (SOM 1 ) _49,350__(carry) LOSS: 650 lb/ac or 1.3% of SOM 0

EXAMPLE 2B WORKSHEET CALCULATIONS For FOUR YEAR ROTATION YEAR 1 TILLAGE: Conventional, once in the late spring, once in fall K 1 : 3.9 % (increase by 30% for additional tillage) CROP: Silage 1000 lb/ac residue; k 2 = 0.75 COVER CROP (planted previous fall): Hairy 3000 lb/ac; k 2 = 80% (0.80) COVER CROP (Fall seeding) Cereal rye

Rotational Accumulation Exercise Worksheet Example 2B Organic Matter (SOM 0 )___50,000__Balance Year 1 Subtract SOM 0 x k1 -__1,950____48,050__ Add NA- (NA x k 2 ) silage+__250_____48, 300__ Add NA- (NA x k 2 )(2nd amendment )+__600_____ 49,900__ Hairy vetch Organic Matter at end of Year 1 (SOM 1 ) _48,900__(carry) LOSS: 1100 lb/ac or 2.2% of SOM 0

EXAMPLE 2B WORKSHEET CALCULATIONS For FOUR YEAR ROTATION YEAR 2 TILLAGE: Conventional, once in the late spring K 1 : 3.0 % CROP: 2000 lb/ac residue; k 2 = 80% (0.80) COVER CROP (planted previous fall): Cereal 6000 lb/ac k 2 = 75% (0.75) COVER CROP (Fall seeding) none

Rotational Accumulation Exercise Worksheet Example 2B Organic Matter (SOM 1 )__48,900___Balance Year 2 Subtract SOM 1 x k 1 -__1,907 _____46,993_ Add NA- (NA x k 2 ) soy+__ 400______47,393_ Add NA- (NA x k 2 )(2nd amendment )+__1,500_____48,893_ Cereal rye Organic Matter at end of Year 2 (SOM 2 ) __48,896__(carry) CUMULATIVE LOSS: 1,104 lb/ac or 2.2% of SOM 0

YEAR 3 TILLAGE: Conventional, once in the late spring, once in fall K 1 : 3.9 % (increase by 30% for additional tillage) CROP: Grain 5000 lb/ac residue; k 2 = 70% (0.70) COVER CROP (planted previous fall): none COVER CROP (Fall seeding) Cereal rye EXAMPLE 2B WORKSHEET CALCULATIONS For FOUR YEAR ROTATION

Rotational Accumulation Exercise Worksheet Example 2B Organic Matter (SOM 2 )___48,893__Balance Year 3 Subtract SOM 2 x k 1 -_1,906______46,987_ Add NA- (NA x k 2 ) grain corn+_1,500_____48,487_ Add NA- (NA x k 2 )(2nd amendment )+____0______48,487_ Organic Matter at end of Year 3 (SOM 3 ) _48,487___(carry) CUMULATIVE LOSS: 1,513 lb/ac or 3% of SOM 0

EXAMPLE 2B WORKSHEET CALCULATIONS For FOUR YEAR ROTATION YEAR 4 TILLAGE: Conventional, once in the late spring K 1 : 3.0 % CROP: 2000 lb/ac residue, k 2 = 0.80 COVER CROP (planted previous fall): Cereal rye, k 2 = 0.75 COVER CROP (Fall overseeding) Hairy vetch

Rotational Accumulation Exercise Worksheet Example 2B Organic Matter (SOM 3 )__48,847___Balance Year 4 Subtract SOM 3 x k1 -__1,455_____47,032__ Add NA- (NA x k 2 ) soy+___400_____47,432__ Add NA- (NA x k 2 )(2nd amendment )+__1,500_____48,932__ Cereal rye Organic Matter at end of Year 4 (SOM 4 ) __48, 932__(carry) TOTAL LOSS AFTER 4 YEARS: 1,068 lb/ac or 2.14% of SOM 0 TOTAL LOSS AFTER 8 YEARS: 2,115 lb/ac or 4.23% of SOM 0

WAYS TO INCREASE OM REDUCE K 2 REDUCE K 2 REDUCE K 1 REDUCE K 1 INCREASE NA INCREASE NA

Best Ways to Reduce K 1 Reduce intensity of tillage Reduce intensity of tillage Reduce frequency of tillage Reduce frequency of tillage Reduce depth of tillage Reduce depth of tillage Reduce area of tillage (e.g. zone till) Reduce area of tillage (e.g. zone till) Reduce mechanical cultivation (uh oh!) Reduce mechanical cultivation (uh oh!)

BEST WAYS TO LOWER K 2 Species / amendment choice Species / amendment choice Allow covers to grow longer Allow covers to grow longer All other factors are already rolled into k1 All other factors are already rolled into k1

BEST WAYS TO INCREASE NA Plant cover crops in timely way Plant cover crops in timely way Allow cover crops to grow longer Allow cover crops to grow longer Fill short niches with covers Fill short niches with covers Full-year fallow with cover crops Full-year fallow with cover crops Species choices Species choices Supplement with manure and compost Supplement with manure and compost Use more small grains Use more small grains

TO DO LIST Include manure (k 2 = 0.20 – 0.50) and compost (k 2 = 0.10 – 0.30) Include manure (k 2 = 0.20 – 0.50) and compost (k 2 = 0.10 – 0.30) Develop as Excel worksheet Develop as Excel worksheet Account for OM protection by clays and aggregates Account for OM protection by clays and aggregates Account for “small-grain effect” Account for “small-grain effect” Include more vegetable residues Include more vegetable residues Account for erosion Account for erosion

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