Effect of Nitrogen Sources, Rates, and Application Time On Spring Wheat Yield and Grain Protein.

Nitrogen (N) is a primary constituent of proteins; thus, N nutrition directly and radically impacts spring wheat production profitability. Numerous important questions remain unanswered regarding the optimum fertilization strategies for maximizing spring wheat yield and grain protein. The major objective of this study is to determine the most efficient N fertilizer source, rate, and application time combination for optimizing Montana spring wheat yield while maximizing grain protein and N use efficiency (NUE). This project was funded by the Montana Fertilizer Tax Advisory Committee, initiated in 2011, continued in 2012 at at three dryland locations. Three dryland experiments were established: one at Western Triangel Agricultural Research Center, Conrad, MT, and two in cooperating producers’ fields (Jack Patton, Chouteau County, and Lindsay Martin, Teton County) using Choteau spring wheat variety. A combination of 4 preplant N rates (0, 40, 80, and 120 lbs N ac), 3 topdress N rates (0, 45, and 90 kg N ha-1), 2 topdress N fertilizer sources (granual – urea, 46-0-0, and liquid – urea ammonium nitrate (UAN), 28-0-0), and 2 topdress application times (before flowering and after flowering) were evaluated. Urea was manually broadcasted and UAN was applied as a foliar spray using an ATV-mounted sprayer. Treatment effect (preplant N rate, topdress N source, rate, and application time) on spring wheat grain yield, grain protein, N uptake, and N use efficiency (NUE) were evaluated. There is a need for locally-based field studies that would provide up-to-date, scientifically sound and unbiased information that would help Montana grain producers to make more educated nutrient management decisions. This study will assist crop producers by providing such information based on systematic and comprehensive evaluation of risks and benefits associated with various fertilization practices.