Response of Maize to Cover Crops, Fertilizer Nitrogen Rates, and Economic Return

17 Maize is the world’s most widely grown cereal on the basis of Mg produced (FAO, 2014). Nitrogen fertilizer applied to cropland is a considerable portion of the cost and energy input associated with nonlegume crop production (Liebman et al., 2012). When N is lost from cropland, it represents both a fi nancial loss to producers and has a potentially negative impact on the environment (Vetsch and Randall, 2004). Leguminous cover cropping systems have been proposed as a method to reduce the reliance on fertilizer N and reduce environmental risks by decreasing N losses (Reinbott et al., 2004). Cover crops are steadily gaining adoption by producers across the Great Plains as a cultural practice to improve soil health and crop yields (Dagel et al., 2014). Previous studies have shown that apart from providing N, winter legume cover crops can improve physical soil properties, reduce soil erosion, conserve soil water, recycle plant nutrients, and increase crop yield potential and soil productivity (Veenstra et al., 2007). Th e practical use of winter legume cover crops, however, is oft en limited by the asynchrony of cover crop planting windows and biomass accumulation with planting windows for summer cash crops (Janke et al., 2002). For example, to allow winter legume cover crops adequate growing time before cold temperatures occur, summer crops may need to be harvested before optimum conditions (Blanco-Canqui et al., 2012). A delayed planting date of summer cash crops is also oft en necessary to allow winter legume cover crops adequate time to produce biomass and accumulate N. Early harvest and late planting may reduce the yields of summer cash crops (Blanco-Canqui et al., 2012). Challenges encountered in the use of winter cover crops can be overcome by using adapted tropical legumes. Under favorable climatic conditions, high-biomass-producing and high-Nfi xing summer or tropical legume cover crops such as cowpea, pigeonpea, and sunn hemp may have more rapid and greater eff ects on increasing crop yields and improving soil properties than winter cover crops with low biomass input (BlancoCanqui et al., 2012). Balkcom and Reeves (2005) reported that sunn hemp produced 7.6 Mg ha–1 of biomass with 144 kg ha–1 of N in the fi rst 2 yr in Alabama. Cherr et al. (2006) observed Crop Ecology & Physiology