Evaluating Compost and Cover Crops in Corn Cropping Systems with Stover Harvest.

Corn stover as a bioenergy feedstock will put greater demand on the soil resource and challenge farm managers to engage agricultural practices that avoid C depletion and soil degradation. We have introduced corn stover removal (vs. corn stover retention) into a long-term crop rotation study that uses cover crops and composted dairy manure to enhance nutrient availability and build soil organic matter. In a split/split randomized complete block design, we are evaluating cover crops and/or compost as carbon supplements (offsetting C removed from stover harvest) in two corn cropping systems (continuous corn vs. corn-soybean-wheat). Our preliminary results show the profound influence that “year” (i.e. weather pattern) has on corn plant growth and harvest index (HI is the amount of grain divided by the whole plant biomass). In the past 3 years, the HI of corn has ranged from 45 to 59%. Agricultural models generally use 50% for corn HI, which would overestimate stover biomass by 39% and 50% in 2006 and 2007; however, would underestimate stover biomass by 27% in 2008. It is interesting to note that the year with the lowest grain yield produced the greatest amount of stover biomass. Understanding the relationship among corn grain yield, harvest index, and weather pattern will improve estimates of corn stover production. We hypothesize that stover harvest without cover crops and/or compost will create a negative C balance in both cropping systems; however, stover removal will decrease the immobilization potential associated with corn residue incorporation. Therefore, stover removal may minimize the yield depression of continuous corn and decrease the N fertilizer required to maximize yield (in the short-term). Ultimately, we hope results from this study can be used to quantify the amount of stover that can be sustainably harvested from a variety of soil types and cropping systems.