Influence of Residual Soil Nitrogen on Wheat Production.

Growers are challenged with managing nitrogen (N) to grow wheat for grain, forage or both on approximately 2.43 million hectares per year in Texas. While N impacts potential yield, seed quality, disease, insect management and maturity in wheat, escalating costs of N, volatility in market pricing and loss of applied N to the environment require implementation of strategies that improve nitrogen use efficiency and net return. Previous studies planted to corn and grain sorghum in the Central Blacklands and upper Gulf Coast regions in Texas demonstrated that grain yields and test weights were not affected at 97 and 89 percent of sites, respectively when carryover N was credited to 60 cm, an efficient recovery of profile soil N. Given that roots of winter wheat have been shown to surpass a depth of 1 m in previous studies, it seems likely that wheat producers, too, could successfully credit soil nitrogen. A field study was initiated in the fall of 2015 in the Central Texas Blackland to assess the response of wheat grain yield, seed quality (test weight and protein), and total N content in stover to residual soil nitrate-N to 60 cm. Two weeks before planting, deep profile sampling was used to identify amounts of residual soil nitrate-N to soil depth. At Feekes stage five, supplemental N was top-dress applied to achieve a representative yield goal and soil test recommendations based on residual nitrogen at 0 to 15-, 0 to 30-, 0 to 60-, and 0 to 91cm. Experimental units were arranged in a randomized complete block design and replicated four times. Images of study plots were collected at flowering. Data collected at final harvest will be statistically analyzed and a summary of the results will be presented.