Tillage and nitrogen source and rate effects on corn response in corn-soybean rotation

Conservation tillage systems present a challenge for integrating an efficient fertilizer program for corn (Zea mays L.) production in the U.S. Midwest and elsewhere. The objective of this study was to evaluate corn response to three tillage systems (no-tillage, strip-tillage, and chisel plow) and four N rates (0, 85, 170, and 250 kg N ha(-1)) of liquid swine manure and commercial fertilizer in a corn-soybean [Glycine mar (L.) Merr.] rotation. A 3-yr study from 2002 to 2004 was conducted on a Kenyon soil (fine-loamy, mixed, mesic Typic Hapludoll) at the Iowa State University Northeast Research and Demonstration Farm near Nashua, IA. The experimental design was a randomized complete block with split plots. Tillage and N rates were randomly assigned as main plot and subplot treatments, respectively. Corn grain yield and aboveground biomass response to different tillage systems were not significantly different for all N rates of both N sources; however, the biomass yield at different growth stages with different N sources, tillage, and N rates were inconsistent. There were no interaction effects of tillage and N rates on yields, except in a few cases. The 3-yr average of maximum (MNR) and economic optimal (EONR) N rates (182 and 174 kg N ha(-1) respectively) across all tillage systems with liquid manure produced identical maximum (MGY) and economic optimum (EOGY) grain yields of 11.7 Mg ha(-1). In contrast, the MNR and EONR (176 and 144 kg N ha(-1), respectively) with commercial fertilizer N produced a MGY and an EOGY of 11.2 and 11.1 Mg ha(-1), respectively.