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

Abstract

Abstract 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.