Increased plant nitrogen loss with increasing nitrogen applied in winter wheat observed with (15)nitrogen

Nitrogen (N) fertilizer is generally the most costly input for winter wheat (Triticum aestivum L.) production. Therefore, it was important to maximize fertilizer use efficiency and minimize N losses to the environment. One of the mechanisms responsible for decreased N use efficiency (NUE) was plant N loss. The objectives of this experiment were to determine fertilizer N re covery in winter wheat when produced for forage and grain, and to quantify potential plant N losses from flowering to maturity in winter wheat. Two lo ng-term (>25 years) winter wheat (Triticum aestivum L.)N sate fertility exp eriments (Experiment 222 and Experiment 502) were selected to evaluate N-15 fertilizer recovery. Percent N-15 recovery was determined from all micropl ots in plant tissue at flowering, in the grain, and straw at harvest and in the soil. Fertilizer N ((NH4)-N-15 (NO3)-N-15) was applied at rates of 0, 45, 90, and 135 kg N ha(-1) in Experiment 222, and 0, 22, 45, 67, 90, and 1 12 kg N ha(-1) in Experiment 502. The ratio of NO3- to NH4 (+) in wheat for age at flowering was positively correlated with estimated plant N loss. Est imated plant N loss (total N uptake in wheat at flowering minus N uptake in the grain and straw at maturity) ranged from a net gain of 12 kg N ha(-1) to a loss of 42 kg N ha(-1), and losses increased with increasing N applied .