Nitrogen fertilization of conservation-tilled wheat. I. Sources and application rates

Selection of the nitrogen (N) source and rate for application is critical to ensure profitable wheat (Triticum aestivum L.) yields. The research objective was to evaluate several N sources and spring application rates for conservation tillage wheat production. Research was initiated in the fall of 1997 and continued through 2000 on Collins silt loam (Aquic Udifluvents). A different cultivar was seeded each of the three years. The experimental design was a split-plot with 0, 34, 67, 101, 134, and 168 kg N ha(-1) rates the main plots and N sources (ammonium nitrate, urea, urea-ammonium nitrate, ammonium sulfate and UAN + Ca(NO3)(2) co-mixture) the sub-plots. The yield response to N rate varied with year and N source. For the three years, yields were increased by applying either 67 or 101 kg N ha(-1) Broadcasting AN produced higher yields than urea-containing N sources (urea or UAN) for two of the three years. Broadcasting urea or UAN restricted yields approximately 12% apparently due to N volatilization losses. Broadcasting AS was as effective as AN one of the two years while broadcasting the UAN + Ca(NO3)(2) co-mixture resulted in higher yields at a lower N rate than AN for one of two years. Yield differences due to N source were small when rainfall occurred within two days of soil application. Take-all root rot affected yield one of three years with AN and AS being more efficient N sources. Sulphur fertilization was not needed for wheat production on this soil.