Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2006
Publication Date: 7/6/2006
Citation: Hoskinson, R., Karlen, D.L., Birrell, S.J., Radtke, C.W., Wilhelm, W.W. 2006. Engineering, nutrient removal, and feedstock conversion evaluations of four corn stover harvest scenarios. Biomass and Bioenergy. 31(2-3): 126-136. Available: http://www.sciencedirect.com/science?
Interpretive Summary: The U.S. Department of Energy (DOE), Office of Biomass Program (OBP), plans to accelerate the use of agricultural residue as a near-term source of biomass for renewable fuel, heat, power, chemicals and other bio-materials. Corn stover (the portion of the plant left in the field after the grain is harvested) is expected to be the primary crop residue harvested for these uses. Before this can be done commercially, research is needed to determine how much stover can be removed, how to efficiently harvest the stover, and if there are large differences among the various plant parts (e.g., leaves, stalks, cobs, etc.). The potential effects of harvesting these residues on nutrient removal also need to be determined. We found that harvesting at the normal height (approximately 16 inches high) would provide the amount of crop residue projected from long-term yields. Using 2006 fertilizer prices, we calculated that the cost to replace the nutrients removed with the stover to be $23.21 per acre or $10.22 per ton of biomass. We also found that harvesting the upper portion of the plant (including the cobs) provided the best material for producing bioenergy and that harvesting the lower portion of the corn plant increased the water content and reduced the quality of the stover for producing ethanol. This information is very important for DOE engineers, research scientists, investors, and others interested in developing products from renewable plant biomass.
Technical Abstract: Crop residue has been identified as a near-term source of biomass for renewable fuel, heat, power, chemicals and other bio-materials. A prototype one-pass harvest system was used to collect residue samples from a corn (Zea mays L.) field near Ames, IA. Four harvest scenarios (low cut, high-cut top, high-cut bottom, and normal cut) were evaluated and are expressed as collected stover harvest indices (CHSI). High-cut top and high-cut bottom samples were obtained from the same plot in separate operations. Chemical composition, dilute acid pretreatment response, ethanol conversion yield and efficiency, and thermochemical conversion for each scenario were determined. Mean grain yield in this study (10.1 Mg ha-1 dry weight) was representative of the average yield (10.0 Mg ha-1) for the area (Story County, IA) and year (2005). The four harvest scenarios removed 6.7, 4.9, 1.7, and 5.1 Mg ha-1 of dry matter, respectively, or 0.60 for low cut, 0.66 for normal cut, and 0.61 for the total high-cut (top + bottom) scenarios when expressed as CHSI values. The macro-nutrient replacement value for the normal harvest scenario was $57.36 ha-1 or $11.27 Mg-1. Harvesting stalk bottoms increased stover water content, risk of combine damage, estimated transportation costs, and left insufficient soil cover, while also producing a problematic feedstock. These preliminary results indicate harvesting stover (including the cobs) at a height of approximately 40 cm would be best for farmers and ethanol producers because of faster harvest speed and higher quality ethanol feedstock.