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

Nitrogen (N) is considered the most common nutrient limiting yield of spring wheat and other cereal crops in Montana. Wheat production represents almost 25% of total Montana’s agricultural revenue. Protein content is the base for established market adjustments for spring wheat, with premiums paid for increase above the baseline levels. Nitrogen 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. Three dryland experiments were established: one at Western Triangle Agricultural Research Center (WTARC) (near Conrad, MT) and two in cooperating producers’ fields (Jack Patton, Knees, Chouteau County, MT, and  Lindsey Martin, Pendroy, Teton County, MT) using Choteau spring wheat variety. A combination of 4 preplant N rates (0, 40, 80, and 120 lbs N ac^-1), 3 topdress N rates (0, 40, and 80 lb N ac^-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 backpack sprayers. Each treatment was replicated 4 times at each location. Treatment effect (preplant N rate, topdress N source, rate, and application time) on spring wheat grain yield, and grain protein content were evaluated using statistical procedures. There is a need for locally-based field studies that would provide up-to-date, scientifically sound and unbiased information that would help 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.