Nutrient and alkalinity removal by corn grain, stover and cob harvest in Upper Midwest USA

In the USA, most corn stover currently remains in fields as crop residue that provides soil erosion control and maintains soil organic carbon levels. This stover is a potential biofuel feedstock for direct combustion, pyrolysis, and ethanol fermentation. At a research site in south central Wisconsin, the northern edge of the US Corn Belt, corn grain harvest averaged 9.8 Mg ha−1 DM over a 6-year period, 1997 to 2002. Removal of all stover could recover an additional 7.2 Mg ha−1 y−1 DM and, in the process, remove an additional 47, 6, 81 and 197 kg ha−1 y−1 of N, P, K and calcium carbonate equivalent, respectively. The fertilizer replacement cost for stover removal is 32 $ Mg−1 DM, which is 95% of the fertilizer value of the grain. However, most of the N, P, K and alkalinity of the stover is found in the leaves, stalk, and husks, not in the cob. At our study site, complete stover removal would export 235 $ ha−1 y−1 of fertilizer and limestone, mainly as K, while cob export would be worth 20 $ ha−1 y−1 in nutrient equivalents. Based on this research, removal of cobs only is equivalent to 16.6% of total stover removal but with a greatly reduced fertilizer replacement cost of 17 $ Mg−1 DM and the same energy density.