The influence of polymer-coated urea and urea fertilizer mixtures on spring wheat protein concentrations and economic returns

The economic benefit of using controlled-release N fertilizers on hard red spring wheat (HRSW, Triticum aestivum L.) depends on its cost/price ratio, grain yield, and availability of discount and/or premium prices for protein concentration. The objective of this study was to evaluate the effect of five different proportions (0, 25, 50, 75, and 100%) of polymer-coated urea (PCU) in the N fertilizer mixture applied at three different N rates on (i) HRSW grain yield and protein concentration and (ii) whole-plant dry matter and total N accumulation, and (iii) also to perform an economic analysis. As the proportion of PCU in the fertilizer mixture increased, the grain yield decreased in Environment 1 and remained the same in Environment 2. Cool dry conditions in Environment 1 delayed N release from PCU causing N deficiencies during the critical yield-development phase and resulting in lower grain yield as the PCU proportion increased. In contrast, this was not the case in Environment 2. As the proportion of PCU in the fertilizer mixture increased, protein concentrations increased in both environments indicating that PCU increases soil-N availability later in the growing season, regardless of the early season weather conditions. The proportion of PCU in the fertilizer mixture did not affect total N accumulation and post-harvest soil NO₃-N concentrations. The results of this study suggest that adding a portion of PCU in the fertilizer mixture can increase HRSW grain protein concentration and provide economic benefits to producers if discount prices are around $20 per Mg or greater.