Organic Material vs Matter Humus Passive OM Organic matter Slow OM Organic material Active OM Organic material is anything that was alive and is now in or on the soil. Organic material is unstable in the soil As much as 90 percent of it disappears quickly because of decomposition. When organic material decays to the point it is no longer recognizable 5 percent of it mineralizes yearly When the organic matter has broken down into a stable humic substances that resist further decomposition
IT MEANS A LOT! Improve water infiltration rate/holding capacityinfiltration rate/holding capacity Supply free nutrients Decrease pests, pollution from pesticides and heavy metals Soil pH bufferpH Improve soil tilth/ structure Reservoir of nutrients and water CEC CEC C sequestration: reduce CO 2 and CH 4 Improve microbial mass and species diversitymicrobial
OM level % WHC, lbsRain,in 4-5165-1954-6 1.5-235-450.5-1.5 If OM<2.5%, N,P and K leach away Water holding capacity NT vs CT Prior et al., 2003 Mielniczuk, 1996 pH Infiltration
... IT MEANS A LOT! Effect on CEC Soil particleCEC (cmol/kg) Humus100-300 Smectites (black swelling clays) 60-150 Kaolinite (white clay)2-15 Fe and Al oxides (from ferrosols) <1 McLaren and Cameron (1996). Gardener et al.,2002; composting and compost proceeding Effect on microbes, dairy manure
Low C:N ratios (<20:1) o mineralization and rapid rates of decomposition o Undiluted manure and blood meal, grass clippings, vegetable wastes High C:N ratios (>30:1) o immobilization and slower decomposition rates o Straw, bark, wood chips, sawdust, paper, cornstalks, foliage Intermediate C:N materials (20:1 – 30:1) o Most composts, leaf mulches, cover crop residues Organic Material Decomposition
First thing first! What is the goal? o Short-term nutrient supply o Slow nutrient supply Highly decomposable material vs slow decomposing materials Nature of the organic enterprise Soil type and problem
Building Soil OM 3-Strategies 1. Decrease losses 2. Add Organic Material/Matter 3. Consider Sustainability
1. Building Soil OM: decrease losses Reduce tillageErosion control Corn, Hussain et al., 1999, SSSAJ Schertz et al., 1984, ASAE, proceeding
1. Cover Crops Spring Annuals o Oats and Triticale. Summer Annuals o Buckwheat, Cowpea, and Sorghum Winter Annuals o Austrian Winter Pea, Hairy Vetch and Winter Rye are planted in late summer/early fall, over winter, and resume growing the following spring. Biennials: o Yellow Blossom Sweet clover and perennials Red Clover can be grown for longer term soil-building.
... Cover crops Ability of cover crops to scavenge nitrogen (N) in the fall and decrease leaching.
... Cover Crops Common C:N ratios of cover crops Organic MaterialC:N RatioReference Young rye plants14:1 (Sarrantonio, 1994) Rye at flowering20:1 (Sarrantonio, 1994) Hairy vetch10:1 to 15:1 (Sullivan, 1990) Crimson clover15:1 (McLeod, 1982) Corn stalks60:1 (Sarrantonio, 1994) Sawdust250:1 ((McLeod, 1982) If we return 2.2 tons/ac/yr of residue to the soil, it will maintain soil OM at constant level in continuously cropped soils.
2. Green manure Non-legumes: supply OM Legumes o Both OM and fix N o Legumes add 25-70 lbs N/ac
... Green Manures Biomass and N yields of winter annual GM crops Cover CropBiomass tons/acreNitrogen lbs/acre Sweet Clover1.75120 Berseem clover1.1070 Crimson Clover1.40100 Hairy Vetch1.75110 “Green manure crops can supply an OM equivalent of 9 to 13 tons per acre of farmyard manure or 1.8 to 2.2 tons dry matter per acre.” However, the benefit from green manure crops’ soil benefits will be gone in a year or less. Schmid and Klay, 1984
3. Animal Manure TypeN, lbs/t P, lbs/tK, lbs/tSolids % % PAN yr1 B density lbs/cu yard Dairy solids 512200-201100 Beef feedlot 123142520-401400 Broiler litter 7328557040-70900 Laying hen 372539401400 Horse 9313350-201400 Sheep 184.029281400 Species, feed, and handling dependent
4. Compost Low in nutrient Low availability More of OM buildup Very easy procedures available Any organic material can be composted Materials vary
Compost vs Manure? CompostManure slow release form of nutrients usually higher nutrient content easier to spread sometimes difficult to spread higher investment of time or money lower investment of time or money lower potential to degrade water quality higher potential to degrade water quality less likely to contain weed seeds more likely to contain weed seeds reduced pathogen levels potential for higher pathogen levels more expensive to purchase less expensive to purchase fewer odors odors sometimes a problem improves soil tilth
5. Uncomposted Yard Debris Nutrient rich/poor, depends on material Better than compost Grass clippings release nutrients quickly; 20 lbs N/wet ton, 5-20% is available Wood takes for ever! Leaves and small branches decompose quickly
6. Packaged Organic Fertilizers Easy to use Less variable More concentrated Expensive! Blended forms Organic FertN, (%DW) P 2 O 5, (%DW) K 2 O (%DW) Feather meal1-21-3 Steamed bone meal7-1320-30<1 Dried Kelp1-2<12-15 Seed meal6-72-31-2
Esthetic Good smell No complaint! Drains Soaks well No hard pan Friable Resilience Bulk density Nutrients available Optimum pH High CEC Rich in Soil organisms Diversity Less pests Support continuous production Increased continuous income