CROP INSIGHTS Sustainable Corn Stover Harvest for Biofuel Production by Mark Jeschke and Andy Heggenstaller, Agronomy Research Managers Summary • Corn stover is the most plentiful source of lignocellulosic biomass in the U.S. Sustainable utilization of corn stover as a feedstock for ethanol and other biofuels could help meet energy needs while delivering agronomic benefits. • In fields where excess residue interferes with planting, impedes stand establishment, and ties up nitrogen, partial stover harvest can increase corn yields and potentially reduce production costs. • Sustainable corn stover harvest requires that only a portion is removed from the field, leaving a sufficient amount behind to meet other critical needs, including mitigation of soil erosion, maintenance of soil organic matter, and sustained soil fertility. Higher corn yields have been accompanied by increases in corn residue. Harvesting excess stover for ethanol pro- • The amount of stover that can be sustainably harvested is duction is a way to capture additional value from the crop generally most limited by the amount that must be left in while reducing residue management challenges. the field to maintain soil organic matter levels. Sustainable corn stover harvest must be done in such a way • Crop nutrients, most notably potassium, are removed as to provide value to the grower and biofuel producer from the field when stover is harvested. Specific removal without negatively impacting the health and productivity of rates will vary according to soil nutrient levels, growing the soil. Stover removal is not an option for every field, conditions, hybrid, and the time and method of harvest. particularly those subject to erosion or those with low average yields and low stover production. On the other Introduction hand, stover harvest may offer stand establishment and yield advantages for uniform, high yielding fields with high levels Lignocellulose is a structural component of all plant matter. of corn residue that impede crop production. Weighing the Because it is abundant in nature, has high energy value, and crop production advantages versus the value of the residue is not used directly for human consumption, this material removed can help growers make a profitable and sustainable holds great promise for renewable energy production. The decision for each field. primary plant materials being considered for large-scale cellulosic ethanol production include crop residues, “energy Value of corn stover in a cropping system crops” developed specifically for fuel, and forest and wood processing residues. Of these, crop residues, and particularly Corn residue plays several important roles in a cropping those of corn, hold the greatest potential (U.S. Department system. Its most obvious function, and the primary driver of Energy, 2011). behind the historical trend toward reduced and no-tillage, is Corn produces the highest volume of residue of all the mitigating wind and water erosion. Return of corn residue to major crops in the U.S., and this volume has increased in the soil is also important in maintaining soil organic matter, tandem with corn grain increases. Because of its abundance which in turn influences soil structure, fertility, and water and even excess in some areas, several “second-generation” holding capacity. Because of the value that corn residue ethanol plants that use corn residue as a feedstock are provides in maintaining soil productivity and maximizing planned for production in the U.S. Corn Belt. This will grain yields, a sustainable corn stover harvest program provide growers with the opportunity to get more value necessarily only removes a portion of the total corn stover, from their agricultural land by supplying corn stover to leaving a sufficient amount behind to meet critical needs make biofuel. (erosion control, fertility, soil carbon, etc.). • VOL. 22 • NO. 5 • PAGE 1 PIONEER AGRONOMY SCIENCES CROP INSIGHTS ®, SM, TM Trademarks and service marks of Pioneer Hi-Bred International, Inc. ©2012, PHII Corn residue higher, often excessive production is not substantially different than tilling the soil to increase decomposition (Al-Kaisi and Yin 2005). The level of corn residue remaining in the spring has In cases where management of excess residue is a driving increased significantly in many fields as a result of the factor in management decisions, partial stover harvest could general trend for higher corn yields (Figure 1). Management potentially expand rotation and management options. For of corn residues has become more difficult due to the use of example, a reduction in excess residue could allow for foliar fungicides and Bt traits that result in stronger corn increased production of corn following corn, particularly in stalks that resist decomposition. Adoption of reduced tillage the northern Corn Belt where residue decomposition tends practices has also contributed to less residue breakdown in to be slower. Tillage or other field operations currently done many areas. Corn produced in the U.S. Corn Belt has specifically to manage residue could potentially be maintained a relatively stable harvest index of 0.5, meaning eliminated, providing substantial production cost savings. that increases in grain yield have been accompanied by Partial stover harvest could have secondary benefits as well, corresponding increases in stover production (Lorenz et al. including reduction in inoculum levels for corn pathogens 2010). that overwinter in corn residue (e.g., anthracnose, gray leaf 450 10.7 spot, Goss’s wilt, and northern leaf blight) as well as Yield Record: 429 bu/acre reduced nitrogen immobilization. 400 9.5 Stover Yield ) 350 NCGA National 8.3 Residue Management Yield Contest /acre 300 Winners 2006-2011 7.1 Research conducted by the bu ( 250 5.9 University of Missouri and (tons/acre Pioneer Hi-Bred compared 200 4.7 several common methods 150 3.6 of managing residue in 100 2.4 ) no-till continuous corn Grain Yield Yield Grain History 50 1.2 including (1) use of row FAPRI Baseline cleaners at planting, 0.0 0 (2) fall nitrogen application, (3) fall stalk chopping and (4) baling and removing 50% 1966 1970 1974 1994 1998 2002 2006 2010 2014 2018 1978 1982 1986 1990 of stover following grain harvest. Over the four year Figure 1. Average U.S. corn grain and stover yields and duration of the experiment, only the 50% stover removal recent NCGA contest-winning yields. Estimates of corn treatment provided a significant yield advantage compared stover yield are based on a harvest index of 0.5. to no residue management (Figure 2). This outcome was partially explained by improved stand establishment In many highly productive systems, particularly under following stover removal (data not shown), but was also continuous corn, corn stover production most often exceeds likely due to reduced nitrogen immobilization and enhanced the minimum amounts needed to maintain soil health and early corn growth. productivity, making sustainable stover harvest a viable option. In systems where excessive residue levels have 180 become a management challenge, removing a portion of the 174 residue should have a positive impact on stand 170 establishment, early growth and grain yield. 160 157 Advantages of removing excess residue 150 154 151 152 The primary advantage in reducing surface residue is 140 preventing its interference with planting and stand Grain Yield (bu/acre) Yield Grain establishment of the subsequent crop. In many high-yielding 130 areas of the U.S. Corn Belt, residue accumulation has become an increasing problem. To counter this problem, 120 many growers are chopping stalks during or after harvest None Row Fall N Fall Stalk Bale and and/or incorporating stalks into the soil through more Cleaners Chop Remove aggressive tillage. Both practices increase microbial Residue Management degradation of stalks with resulting loss of carbon through CO2 release. From a carbon sequestration standpoint, Figure 2. Effect of residue management practices on grain managing excess residue by removing a portion for ethanol yield in no-till continuous corn (Wiebold, 2011). • VOL. 22 • NO. 5 • PAGE 2 PIONEER AGRONOMY SCIENCES CROP INSIGHTS ®, SM, TM Trademarks and service marks of Pioneer Hi-Bred International, Inc. ©2012, PHII Nitrogen Availability Soil Moisture and Temperature One of the major impacts of excess corn residue is reduced Reducing the amount of nitrogen availability as a result of microbial uptake and residue on the soil surface is immobilization. In order to break-down crop residues, soil generally associated with in- microbes require a nitrogen source. While this immobilized creased soil temperature in the nitrogen is later released back to the soil as microbial spring and a faster rate of soil populations decline, it is unavailable during spring and early drying, which can be advan- summer when crop nitrogen demands are highest. For tageous in many cases. Higher residues that have a carbon-nitrogen (C:N) ratio less than soil temperatures in the spring 30, ample nitrogen for microbial decomposition is derived will almost always be positive, directly from the residue itself and no immobilization since soil temperatures at occurs. This is the case for soybean residues as well as for planting are often below the most animal manures. For residues and other organic optimum levels for germination amendments that have a C:N ratio greater than 30, and emergence. Warmer soil additional nitrogen required for decomposition is derived temperatures can improve from soil mineral nitrogen that would otherwise be available germination as well as subsequent root growth and nutrient for crop uptake. Corn residues typically have a C:N ratio in uptake. the range of 50-75 and can immobilize large quantities of Faster soil drying is usually positive, especially in northern nitrogen, especially at high residue levels. states and northern areas of central states where wet spring Research conducted at the University of Illinois conditions often prevail. Faster drying soils allows growers demonstrated the value of corn stover harvest as means of to get into the field sooner for spring tillage, fertilizer reducing nitrogen immobilization and fertilizer nitrogen application and planting.