Broadcast Nitrogen Sources for No-Till Continuous Corn and Corn Following Soybean

Studies evaluating surface broadcast urea-based N sources in no-till corn (Zea mays L.) have been primarily conducted with continuous corn. Most corn grown in Missouri follows soybean [Glycine max (L.) Merr.]. Our objective was to evaluate no-till, continuous corn and corn following soybean response to surface applied ammonium nitrate (AN) and urea-based N sources. Field studies were conducted at three Missouri sites during 1988–1990. Factorial combinations of rotation (continuous corn and corn-soybean) N source [AN, urea, urea ammonium nitrate (UAN), and UAN + ammonium thiosulfate (UAN + ATS)], and N rate (67, 135, and 202 kg ha⁻¹) were studied in a split-block design. Nitrogen rate and source affected grain yields each site-year. Ammonium nitrate was superior to the urea-based N sources in 5 of 8 site-years. Averaged across site-years, grain yields (Mg ha⁻¹ were 8.22 for AN, 7.57 for urea, 7.09 for UAN + ATS, and 6.99 for UAN. Apparent fertilizer N losses were estimated at 11% for urea, 18% for UAN and 17% for UAN + ATS. Ammonium thiosulfate did not improve the performance of UAN. Grain yield responses to applied N were greater with continuous corn than corn following soybean. Continuous corn also resulted in larger yield differences between N sources. In continuous corn, AN resulted in greater grain yield than urea by 0.81 Mg ha⁻¹, than UAN by 1.35 and Mg ha⁻¹, and than UAN + ATS by 1.32 Mg ha⁻¹. For corn following soybean, the yield advantage for AN was 0.42 Mg ha⁻¹ greater than urea, 0.98 than UAN, and 0.82 than UAN + ATS. Therefore, reduced fertilizer efficiency of surface applied urea-based N sources appears to be a problem in both continuous no-till corn and no-till corn following soybean. Supported in part by a grant from the Missouri Fertilizer and Ag. Lime Advisory Council. Contribution from the Missouri Agric. Exp. Stn. Journal Series No. 11734.