Published on December 31, 2007
How much corn stover can be removed for biofuel feedstock without compromising soil quality and erosion concerns?: How much corn stover can be removed for biofuel feedstock without compromising soil quality and erosion concerns? Dan Walters and Haishun Yang Dept. Agronomy & Horticulture, UNL Ethanol Production: Ethanol Production Ethanol Production Potential: Ethanol Production Potential Corn Grain (starch) Ethanol = 2.7 gal/bu Corn Stover (cellulosic) Ethanol = 70 gal/ton Grain yield = Stover Yield (Harvest Index = 0.5) Ethanol Production Potential: Ethanol Production Potential Potential ethanol production for a 200 bu/acre corn crop assuming harvest of 100% of stover Grain Ethanol : 540 gal / acre Cellulosic Ethanol : 330 gal / acre 870 gal / acre An increase of 61% if all stover is harvested Slide5: Source: Graham et al. Agronomy J. 99:1-11(2007) Corn-belt Stover Production: Corn-belt Stover Production Source USDA. Assumes average harvest index of 0.5 & 9.2 billion bushels Stover Harvest Technologies: Stover Harvest Technologies Current harvest technologies limit collection to no more than 75% of stover Bale windrow only = 38% Rake and bale = 50-55% Mow, rake and bale = 65-75% Montross et al. ASAE 2003, Stover Harvest Technologies: Stover Harvest Technologies 1 Mg/ha = 0.45 ton/acre Bale windrow Rake/windrow & bale Shred/rake & bale 150 bu/a Graham et al. Agronomy J. 99:1-11(2007) Importance of Crop Residues: Importance of Crop Residues Energy and Nutrient Cycling Every ton of stover contains approximately 10 lb N, 2 lb P, and 45 lb K Provides energy for microbial activity Source of Soil Organic Matter (SOM) Provides structural stability to soil aeration, water infiltration, erosion prevention Nutrient retention Sequestration of N, P and K against loss Importance of Crop Residues: Importance of Crop Residues Water Conservation Water retention of soil increases as a soil organic matter increases Surface residue reduces soil temperature and evaporative loss of water SOM Major source of cation exchange capacity Important to groundwater quality Buffers soil against pH change and nutrient loss Potential Corn Stover Supplies : Potential Corn Stover Supplies Graham et al. 2007. Agronomy J. 99:1-11 Assessed corn stover supplies for cellulosic biomass after consideration of: Residue needed to reduce the hazard of wind and water erosion to the established “T” (tolerance) value (~5 ton/acre/yr) Residue effects on soil water conservation and nutrient removal effects on fertilizer replacement costs. Residue removal rates allowed under current tillage/cropping regimes OR under universal no-till adaptation. No consideration given to soil organic matter maintenance Slide12: Source: Graham et al. Agronomy J. 99:1-11(2007) Slide13: Source: Graham et al. Agronomy J. 99:1-11(2007) Slide14: Source: Graham et al. Agronomy J. 99:1-11(2007) Major Corn Stover Supply Regions: Major Corn Stover Supply Regions Source: Graham et al. Agronomy J. 99:1-11(2007) Regions capable of supplying 1800 ton / day supply ~ 0.6 million ton / yr Slide16: Source: Graham et al. Agronomy J. 99:1-11(2007) How much residue must be returned for productivity concerns?: How much residue must be returned for productivity concerns? We know that soil organic matter is a reflection of soil productivity. Very few studies, however, have been carried out to quantitatively measure and evaluate the relationship between soil type, climate and management on the amount of residue C input needed to sustain SOM and productivity. Model Simulations: Model Simulations DK C & N model Allows simulation of soil carbon change over time using long-term weather data soil physical properties substrate specific decay constants for different residue types and soil humus (old C) Slide20: Declining of SOC with different initial SOC levels with NO C inputs Lincoln, NE Medium texture soil Conv. Tillage No water constraints Slide21: SOC dynamics with 30% of stover removal at different yield levels and initial SOC contents Years SOC, % Slide22: SOC dynamics with 60% of stover removal at different yield levels and initial SOC contents Years SOC, % SUMMARY: SUMMARY Under current production practices, the residue requirements for wind / water erosion control and water conservation, less than 28% of corn stover could be sustainably collected (54 million ton yr-1 = 4.3 billion gallons ethanol) Of this quantity, 60 % is located in regions that can supply an economically sized facility. SUMMARY: SUMMARY Universal adaptation of no-tillage would increase the annual yield to 96 million tons or 7.6 billion gallons of ethanol. Little quantitative information exists relating the amount of annual residue inputs required to maintain soil organic C levels. SUMMARY: SUMMARY Decomposition models suggest that soils with higher indigenous productivity (higher SOM) will also require greater quantities of residue input to sustain SOM and soil productivity. This has been verified in a small number long-term residue removal studies.