Effects of site-specific factors on corn stover removal thresholds and subsequent environmental impacts in the Upper Mississippi River Basin

Abstract

Corn (Zea mays L.) stover removal thresholds are subject to many site-specific factors. Current data do not provide practical stover removal guidelines for given site-specific conditions. We used the Agricultural Policy Environmental Extender (APEX) model to assess the effects of site-specific factors and corn stover removal from 3,703 farm fields within the Upper Mississippi River Basin (UMRB). From among the many management and resource attribute factors across these farm fields, we chose the site-specific factors of two land types (highly erodible land [HEL] and non-HEL), three soil textures (clayey, loamy, and sandy), four hydrologic groups (A, B, C, and D), and two management scenarios (Baseline and Enhanced Conservation Treatment) to characterize the variability of stover production potential. The Baseline management reflects farmer management practices reported in the Conservation Effects Assessment Project National Cropland Assessment database, while the Enhanced Conservation Treatment reflects additional conservation practices and management scenarios needed to mitigate sediment, nutrient, and soil organic carbon (SOC) losses. For evaluation purposes, we used the Conservation Effects Assessment Project National Cropland Assessment “acceptable planning criteria” but with more stringent SOC criteria, which does not allow stover removal on sites that lose SOC. Overall, grain and stover yields and N and P losses decreased, while sediment and SOC losses increased with increasing stover removal. On average, Baseline stover yields on HEL were slightly lower than on non-HEL, while yields were higher on loamy, followed by clayey, and then sandy soils. Hydrologic group D soils had the highest Baseline stover yields, followed by those in group B, then group C, and then group A with the lowest yields. The Enhanced Conservation Treatment management drastically mitigated sediment and nutrient losses by 69% and 57%, respectively. Differential impacts of stover removal were most pronounced among the soil textural classes, followed by soil hydrologic groups, and then land type. Overall, the findings of this research underscore the importance of site-specific factors in determining corn stover removal thresholds. For the Upper Mississippi River Basin and for sites meeting the “acceptable planning criteria,” sufficiently “safe” corn stover removals are possible such that only a portion of the available corn acreage would be required to produce enough ethanol to exceed the National 2012 Energy Independence and Security Act goal. However, we do not evaluate issues associated with ethanol plant economic feasibility, such as spatial concentration of stover production.