Effects of N Fertilization on Yield, Growth, and Extraction of Water by Wheat Following Soybeans and Grain Sorghum1

Abstract

AbstractNitrogen fertilization is an important part of wheat (Triticum aestivum L.) production. It is especially important in double‐crop wheat production because the N system is influenced by previous crop residue. Our objective was to evaluate topdressed rates of 0, 34, 68, 102, and 136 kg N ha−1 as ammonium nitrate spring‐applied to soft red winter wheat (‘Arthur’) grown in double‐cropping sequence following soybeans [Glycine max (L.) Merr] or grain sorghum [Sorghum bicolor (L.) Moench]. The soil was Okolona silty clay (a fine montmorillonitic, thermic Typic Chromudert). We also evaluated a 34 kg ha−1 rate of fall‐applied N with topdressed rates in the spring bringing total N to the same levels as the single spring‐applied topdressed rates above. The effects of previous crop on grain yield, straw yield, plant height, and N uptake were pronounced. All of these were significantly higher following soybeans. We attributed this to greater availability of N following soybeans, but have not ruled out the possibility of a phytotoxic effect associated with grain sorghum residues. There was yellowing and stunting of early wheat growth following grain sorghum across all N rates, regardless of whether fall N was applied or not. This early depression may have led to yield differences that were not completely overcome by the conditions of this study. Depletion of soil water was related to N uptake and yield. Soil moisture from anthesis throughout grain filling decreased progressively faster under wheat that received high rates of N.