Effect of Preplant Irrigation, Nitrogen Fertilizer Application Timing, and Phosphorus and Potassium Fertilization on Winter Wheat Grain Yield and Water Use Efficiency

Preplant irrigation can impact fertilizer management in winter wheat. The objective of this study was to evaluate the main and interactive effects of preplant irrigation, N fertilizer application timing, and different N, P, and K fertilizer treatments on grain yield andWUE. Several significant two-way interactions and main effects of all three factors evaluated were observed over four growing seasons for grain yield andWUE. These effects could be described by differences in rainfall and soil moisture content among years. Overall, grain yield andWUE were optimized, if irrigation or adequate soil moisture were available prior to planting. For rain-fed treatments, the timing of N fertilizer application was not as important and could be applied before planting or topdressed without much difference in yield. The application of P fertilizer proved to be beneficial on average years but was not needed in years where above average soil moisture was present. There was no added benefit to applying K fertilizer. In conclusion, N and P fertilizer management practices may need to be altered yearly based on changes in soil moisture from irrigation and/or rainfall.