BIOGEOCHEMICAL PROCESSES INFLUENCING FORMATION AND STABILIZATION OF SOIL ORGANIC MATTER AND SOIL STRUCTURE
Location: Soil, Water, and Air Resources Research Unit
Title: A five-year assessment of corn stover harvest in central Iowa, USA
Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 28, 2011
Publication Date: September 1, 2011
Citation: Karlen, D.L., Birrell, S.J., Hess, J. 2011. A five-year assessment of corn stover harvest in central Iowa, USA. Soil & Tillage Research. 115-116:47-55.
Interpretive Summary: Corn stover is the above ground material left in fields after corn grain has been harvested. It was identified as a potential feedstock to help meet America's growing bioenergy need. This study reports on the first five years of long-term research being conducted in central Iowa to develop sustainable strategies for corn stover harvest. Collecting cobs and plant parts from the ear upward provided a 5-year average of 3.9 Mg/hectare (1.7 tons/acre) from continuous corn or an average of 4.8 Mg/hectare (2.1 tons/acre) for three harvests from a corn-soybean rotation. Nutrient removal was increased by an average of 29, 3 and 34 kg/hectare (26-2.6-30 lbs/acre) for continuous corn and 42, 3, and 34 kg/hectare (37-2.6-30 lbs/acre) for rotated corn. Use of the Soil Management Assessment Framework to evaluate sustainability using six different indicators showed the soils were functioning at an average of 93 and 83% of their inherent potential at the continuous and rotated sites, respectively. For ethanol production, feedstock quality was much better for the upper half of the corn plant than below the ear because of hight water content, potassium (K) content, and soil contamination. This information will be of value to conservationists, research scientists, the Natural Resources Conservation Service personnel, the Department of Energy, and entrepreurers developing sustainable biomass harvest strategies for the bioenergy industry.
Sustainable feedstock harvest strategies are needed to ensure bioenergy production does not irreversibly degrade soil resources. Our objective was to develop a single-pass combine harvest system for simultaneously gathering corn (Zea mays L.) grain and stover. Our harvest strategies included collecting (1) all above-ground plant material by cutting stalks at a stubble height of approximately 10 cm (whole plant), (2) the upper-half by height, (3) the lower-half by height, or (4) no removal. Stover harvest was evaluated for continuous corn and a corn – soybean [Glycine max. (L.) Merr.] rotation. Collectable biomass from Treatment 2 averaged 3.9 (±0.8) Mg ha-1 for continuous corn (2005 through 2009), and 4.8 (±0.4) Mg ha-1 for the rotated corn (2005, 2007, and 2009). Harvesting stover increased the average N-P-K removal by 29, 3 and 34 kg ha-1 for continuous corn and 42, 3, and 34 kg ha-1 for rotated corn, respectively, when compared to harvesting only the grain. Harvesting only the lower-half of the corn plan required two passes, resulted in frequent plugging of the combine, and provided a feedstock with low quality for conversion to biofuel. Therefore, Treatment 3 was replaced by a “cobs-only” harvest starting in 2009. Structural sugars glucan and xylan accounted for up to 60% of the chemical composition, while galactan, arabinan, and mannose constituted less than 5% of the harvest fractions collected from 2005 through 2008. Soil-test data from samples collected after the first harvest (2005) revealed low to very low plant-available P and K levels which appear to have impacted soybean yield immediately (2006) after the whole-plant harvest strategy was imposed. Average continuous corn yields were 80% of rotated yields with no significant differences due to stover harvest. Rotated corn yields in 2009 after two stover harvests (2005 and 2007) were significantly lower for whole plant and lower-half treatments, presumably because soil-test P was low. A soil quality analysis using the Soil Management Assessment Framework (SMAF) with six indicators showed that soils at the continuous corn and rotated sites were functioning at an average of 93 and 83% of their inherent potential, respectively. We conclude that with good crop management practices, including routine soil-testing, adequate fertilization, maintenance of soil organic matter, sustained soil structure, and prevention of wind, water or tillage erosion, a portion of the corn stover being produced in central Iowa USA can be harvested in a sustainable manner.