Marianne Sarrantonio University of Maine 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 GLUCOSE AMINO ACID H-C-O H-C-OH HO-C-H C-H2OH H R - C – NH2 COOH

Chemical Structure of Plant Compounds LIGNIN

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

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 K1 Baseline for silt loam in temperate climate = approx. 2%/yr Conventional tillage can increase by 50% Additional tillage/ yr can increase by 30% Drought decreases Hot weather increases Light soils increases/ heavy decreases Wet soils (> 60% WFPS) decreases Previous losses of active fraction decreases Large additions to active fraction increases

FACTORS AFFECTING K2 C:N ratio Carbon profile (i.e. % lignin, cellulose, etc.) Age / maturity

Rotational Accumulation Exercise Worksheet Start of Rotation: Organic Matter (SOM0) __________ Balance Year 1 Subtract 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 Worksheet Example 1 Start of Rotation: Organic Matter (SOM0) _50,000____ Balance Year 1 Subtract 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 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

Rotational Accumulation Exercise Worksheet Example 1 Start of Rotation: Organic Matter (SOM0) lb/ac __50,000___ Balance Year 1 Subtract 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)

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

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

Rotational Accumulation Exercise Worksheet Example 2 Start of Rotation: Organic Matter (SOM0) ___50,000__ Balance Year 1 Subtract 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

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)

Rotational Accumulation Exercise Worksheet Example 2A Start of Rotation: Organic Matter (SOM0) _ 50,000___ Balance Year 1 Subtract 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

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 Worksheet Example 2B Organic Matter (SOM0) ___50,000__ Balance Year 1 Subtract 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

EXAMPLE 2B WORKSHEET CALCULATIONS For 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/ac k2 = 75% (0.75) COVER CROP (Fall seeding) none

Rotational Accumulation Exercise Worksheet Example 2B Organic Matter (SOM1) __48,900___ Balance Year 2 Subtract 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

EXAMPLE 2B WORKSHEET CALCULATIONS For FOUR YEAR ROTATION 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

Rotational Accumulation Exercise Worksheet Example 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

EXAMPLE 2B WORKSHEET CALCULATIONS For 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

Rotational Accumulation Exercise Worksheet Example 2B Organic Matter (SOM3) __48,847___ Balance Year 4 Subtract 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 OM REDUCE K2 REDUCE K1 INCREASE NA

Best Ways to Reduce K1 Reduce intensity of tillage Reduce frequency of tillage Reduce depth of tillage Reduce area of tillage (e.g. zone till) Reduce mechanical cultivation (uh oh!)

BEST WAYS TO LOWER K2 Species / amendment choice Allow covers to grow longer All other factors are already rolled into k1

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

TO DO LIST Include manure (k2 = 0.20 – 0.50) and compost (k2 = 0.10 – 0.30) Develop as Excel worksheet Account for OM protection by clays and aggregates Account for “small-grain effect” Include more vegetable residues Account for erosion

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