Bioenergy Feedstocks from Semi Arid Agro ecosystems: Soil C and Water Corporate Sustainability Symposium Kansas State University Daniel Inman*, Neil Hansen, Grace Llyod, May 1, 2012 NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
Overview Biomass production and biofuels o US and regional perspective o Potential environmental pitfalls Large scale field study in Colorado o Rationale and background o Findings NREL s system dynamics water footprint model o Overview and prospectus 2
Crop residues are an important near term feedstock Globally, circa 820 6 Mg (3.2 10 Bushels) of corn grain are produced annually (FAO STAT, 2010). The BTS 2 (US DOE, 2011) estimates that in the US, corn stover is the most abundant agricultural residue, with 170 6 256 6 tons annually. Removal of stover as well as other residues has been reported to have deleterious effects on the soil. Several studies have suggested that removing stover and/or other crop residues will negatively impact soil carbon as well as other soil properties and long term crop yields. 3
Stranded resources need to be evaluated Biomass resource assessments focus primarily on the Midwest as the primary source of agricultural residues. Stranded resources do exist that may be able to contribute to meeting national biofuel goals. Making use of some of these stranded resources and/or land bases may add to local agricultural economies. 4
Improved logistics can free stranded biomass More advanced feedstock logistics designs enable stranded or niche resources to be utilized more efficiently. The Western Great Plains is one such area that has potential to supply locally significant volumes of residues and/or bioenergy crops. Corn grain in Yuma County, CO, for example, averaged 206 bu ac 1 in 2011 versus the national average of 147 bu ac 1. 5
Moving the preprocessing to the field is key 6
Improved logistics may lower costs and expand the collection radius significantly 7
Choice of tillage makes a big difference Conventional Tillage No Tillage Source: US DOE, 2011 8
Low water input corn and residue production In Colorado, many farmers are selling and/or entering into long term lease agreements with the many growing municipalities for their water rights. In response to the need to develop economically viable agricultural systems that use minimal water inputs, researchers have begun to look at numerous alternatives. One such study involved the examination of 72 siteyears of soil and crop yield data from a long term dryland cropping experiment. 9
24 year dryland grain & residue production study The field locations were under no till for the duration of the study (24 calendar years). Corn, sorghum, and winter wheat grains and stover/straw were evaluated for biomass production potential. Soil carbon was monitored regularly at multiple locations at each site. RUSLE was used to model erosive soil losses. DayCent was used to model changes in SOC and long term yields in response to variable residue removal. 10
Overall, residue production was higher than anticipated 10000 8000 Corn stover Corn grain Wheat stover Wheat grain kg ha -1 6000 4000 2000 0 10000 8000 Sterling Stratton Walsh Corn stover Corn grain Wheat stover Wheat grain kg ha -1 6000 4000 2000 0 Summit Side Toe 11
Wheat s harvest index was lower than that of corn s 10000 8000 Corn stover Corn grain kg ha -1 6000 4000 2000 100000 8000 Wheat stover Wheat grain kg ha -1 6000 4000 2000 0 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 Year 12
Tolerable soil erosion limits residue removal Annual erosion (Mg ha -1 yr -1 ) 80 60 40 20 Sterling Baling wheat stover Baling corn stover Tolerable soil loss limit 0 Annual erosion (Mg ha -1 yr -1 ) 80 60 40 20 Stratton Baling wheat stover Baling corn stover Tolerable soil loss limit 0 Annual erosion (Mg ha -1 yr -1 ) 80 60 40 20 Walsh Baling wheat stover Baling sorghum stover Tolerable soil loss limit 0 0 20 40 60 80 100 % Removal 13
SOC loss is inevitable under any removal scenario (A) 2900 No removal 50% removal corn stover 50% removal wheat stover 50% removal corn and wheat stover 2700 g C m -2 2500 2300 2100 (B) 2900 No removal 50% removal corn stover 50% removal wheat stover 50% removal corn and wheat stover 2700 g C m -2 2500 2300 2100 1995 2010 2025 2040 2055 2070 Year 14
Removing residue increases soil water loss 20 Simulated water (mm) 10 0-10 -20 Change in water intercepted Change in water evaporated Change in runoff 1990 1995 2000 2005 YEAR 15
Residue removal in the Western Great Plains is limited Water loss, erosion, and soil carbon all limit the amount of residue removal in dryland cropping systems. Because the soils in the Western Great Plains are low in carbon, there is potential to have higher amounts of removable residue than has been estimated for the Midwest. Productive alternative dryland bioenergy crop rotations have been suggested and are under study. If dedicated non grain crops were grown, approximately 2.5 2.7 Mg ha 1 of biomass could be harvested, while still retaining enough residues to maintain soil carbon. o Reduced or elimination of fallow can increase harvested amount 16
Conclusions Careful consideration should be given to developing sustainable biomass production systems. Dryland areas such as the Western Great Plains can contribute to national biomass goals as long as long term soil and water sustainability is considered. 17