Published on January 4, 2008
Crop Residues:Soil Organic Matter, Biofuel, Both?: Crop Residues: Soil Organic Matter, Biofuel, Both? Wally Wilhelm USDA-ARS Lincoln, NE Slide2: Crop residues The good news: The good news Therefore, we have choices! What is (are) the appropriate use (s) of crop residues? We have technology to produce large quantities of residue. Potential uses of crop residues: Potential uses of crop residues Feed Potential uses of crop residues: Potential uses of crop residues Feed Shelter Potential uses of crop residues: Potential uses of crop residues Feed Shelter Industrial feedstock Fiber Building material Biofuel Potential uses of crop residues: Potential uses of crop residues Feed Shelter Industrial feedstock Soil amendment Slide8: The Concept Massive amounts of crop residue produced in US Corn Belt Available source of structural carbohydrate Growers expend time and energy to eliminate residue (?) Collecting residue as biofuel feedstock would save time and energy, as well as address US energy needs How much residue is producedby a crop of corn?: How much residue is produced by a crop of corn? Assumptions: 1. Bushel of corn weighs 56 lb bu-1. 2. Harvest index [grain mass/(grain mass + residue mass)] is 0.50. Harvest index (HI)(rules-of-thumb): Harvest index (HI) (rules-of-thumb) HI = grain yield / biological yield Biological yield = grain yield + stover yield Corn: 0.50 to 0.55 Wheat: 0.40 Soybean: 0.40 to 0.45 Sorghum: 0.48 How much residue is produced by the US corn crop?: How much residue is produced by the US corn crop? 2000 Grain production: 9.97 x 109 bu (x 56) 558 x 109 lb Residue production: 2.79 x 108 ton 2.54 x 108 MT Assumptions: Bushel (bu) = 56 lb Harvest index (HI) = grain / (grain + residue) = 0.50 (grain yield = residue yield) 2001 (est.) Grain production: 9.43 x 109 bu (x 56) 528 x 109 lb Residue production: 2.64 x 108 ton 2.40 x 108 MT What happens to residue returned to the soil?: What happens to residue returned to the soil? Soil organic matter What is residue good for?-as a soil amendment: What is residue good for? -as a soil amendment Soil structure Bulk density, aggregation Erosion control Soil tilth Aeration Water holding capacity Soil temperature Nutrient cycling Ion exchange Buffering capacity Insect/microbial activity Filtration Reducing evaporation Slide14: Where does it come from? Carbon cycle What is soil organic matter?: What is soil organic matter? Decomposed (decomposing) residue Plant, animal, and microbial Organisms Burrowing insects and animals Microorganisms Fungi, actinomycetes, and bacteria Where does it go?: Where does it go? Erosion Wind Water Respiration CO2 Decomposition CO2 Returned to pools Albrecht. W.A. 1938. Loss of soil organic matter and its restoration. Soils and Man. Yearbook of Agriculture. USDA. Washington, DC.: Albrecht. W.A. 1938. Loss of soil organic matter and its restoration. Soils and Man. Yearbook of Agriculture. USDA. Washington, DC. “Attempting to hoard as much organic matter as possible in the soil, like a miser hoarding gold, is not the correct answer. Its (organic matter) value lies in its dynamic nature. A soil is more productive as more organic matter is regularly destroyed and its simpler constituents made usable during the growing season. … The objective should be to have a steady supply of organic matter undergoing these processes (decomposition) for the benefit of the growing crop.” Where does it go?(Decomposition pools): Where does it go? (Decomposition pools) Residues Labile pool Readily decomposed Low C:N ratio Sugar, protein, starch Intermediate pool Resists decomposition Intermediate C:N ratio Cellulose, hemicellulose Resistant pool Very resistant to decomposition High C:N ratio Lignin (Humus) Can we change it?: Can we change it? Residue management Removal Additions Manure (animal and green manure crop) Tillage Mixing Aeration Can we change it? (continued): Can we change it? (continued) Crop selection Species Rotation or crop sequence Crop use (grain, forage, grazing) Management practices Irrigation Fertilization Pest control Planting time, planting density, etc. Can you change it?: Can you change it? (Cambardella and Elliot, 1992) Slide22: Native Sod Site Tillage D, Sidney NE Year Organic C, Mg ha-1 0 to 7.6 cm Slide23: Water Balance Submodel Active SOM Residues Plant Growth Submodel CO2 CO2 CO2 CO2 CO2 CO2 SOM Submodel Climate Soils Topography Management Century Model Slow SOM Passive SOM after Paustian (2001) Slide24: Modeling steps for soil C component of LCA Initialization based on previous Iowa C project - Simulation for major soil types (6-10) for each county - Historical management practices based on CSRA and ancillary data sets Yields calibrated to NASS county averages Corn-soybean with intensive tillage simulated as baseline system. Conversion to continuous corn with: no residue removal residue removal limited by allowable soil erosion rate Three tillage alternatives: 2 mulch tills, 1 no-till after Paustian (2001) Slide25: after Paustian (2001) Slide26: after Paustian (2001) Residue Management Study(1978-1983): Residue Management Study (1978-1983) Background Response to energy crisis of the 70s Objective (question) What is the affect of removing crop residues from (and adding residue additional to) the soil surface On soil properties? On crop production? Residue Management Study: Residue Management Study Over all years (Wilhelm et al., 1986) Residue Management Study: Residue Management Study Soil Water (Wilhelm et al., 1986) Residue Management StudySoil organic matter (0-30 cm): Residue Management Study Soil organic matter (0-30 cm) After 8 yr of treatment application (cont. corn, no tillage) (Maskina et al., 1993) Residue Management StudySummary (production): Residue Management Study Summary (production) Greater plant stress Less available soil water Greater canopy and soil temperature Decreased yield (50% removal) 13% reduction in grain yield 17% reduction in residue yield Yield reductions more closely related to soil water than soil temperature Residue Management StudySummary (Soil organic matter): Residue Management Study Summary (Soil organic matter) Soil organic matter Changed linearly with residue application Remove 100% -5.7% Remove 50% -3.4% No removal ----- Add 50% +4.6% Change in soil organic carbon (SOC) after 13 years of continuous corn (0-15 cm): Change in soil organic carbon (SOC) after 13 years of continuous corn (0-15 cm) (Clapp et al., 2000) Summary (reality?): Summary (reality?) Maintaining soil organic matter levels and yields with residue removal is VERY difficult. There are many more ways to accelerate destruction of organic matter than building it. Field and simulation studies suggest cautious optimism for use of crop residues as biofuel. Clichés : Clichés “Throwing rocks is easy!” (Pat Gruber, CargillDo LLC, Sept. 6, 20001) A bit of skepticism can be a good thing. You can’t have your cake (soil organic matter) and eat (burn) it too. If it sounds too good to be true, it probably is. There are no free lunches. However Rules in the Real World: Rules in the Real World Nature always bats last. Consequences of ignoring rules: “Today's solutions become tomorrow's problems.” (Tom Franzen, Iowa Farmer) Crop Residues:Organic Matter, Biofuel, Both?: Crop Residues: Organic Matter, Biofuel, Both? The good news Large quantities of residue available Production technology exists The bad news Maintaining SOC levels with residue removal is difficult The question SOC or biofuel, both? Dynamics of soil organic matter: Dynamics of soil organic matter Secret to SOM’s pivotal role in soil (crop) productivity Key to its fragile (transient) nature Slide39: Remember, grain pays the bills!