Stover, tillage, and nitrogen management in continuous corn for grain, ethanol, and soil carbon

Interest in harvesting corn (Zea mays L.) cellulosic materials for ethanol production has resulted in the development of research questions regarding its potential effects on crop growth and productivity as well as soil quality. Previous research has generally occurred in environments different than those found in the Upper Midwest, meaning application of those conclusions to the Upper Midwest may not be appropriate. This research is unique because it was conducted on heavy-textured, poorly-drained soils in several tillage systems in environments where soil temperature is often a limiting factor on crop growth. This research indicates corn stover removal in continuous corn cropping (CC) systems improves agronomic performance, but decreases soil C in as little as 3 yr. Agronomic measurements including plant emergence, plant height and normalized difference vegetative index at the eight leaf collar stage, grain yield, stover biomass yield, and stover cellulosic ethanol yield improved with stover removal. The fertilizer N rate needed to economically optimize grain yield decreased by at least 2, 12, and 19 kg N ha-1 for chisel, strip-till, and no-till, respectively. Greater nutrient use efficiency was also often observed with stover removal. In general, the greatest differences in N use efficiency between stover management treatments in the reduced tillage treatments occurred at low fertilizer N rates. This indicates that N availability was less when stover was retained because stover remaining on the soil surface decreased net N mineralization. However, various soil C pools were negatively affected by stover removal, particularly in surface measurements (0 to 15 cm). In contrast, retaining corn stover increased soil C in the same depths. These results indicate that the benefits of stover removal on agronomic performance and the adverse effects on soil C dynamics must be carefully deliberated when considering employing stover removal in CC cropping systems in the Upper Midwest.