I. Effect of nitrogen rate on plant nitrogen loss in winter wheat varieties. II. Glutamine synthetase activity in winter wheat varieties. III. Effect of nitrogen fertilization and cation removal on soilpH

Scope and method of study. Two field experiments were initiated to estimate plant N loss from several wheat (Triticum aestivum L.) cultivars and experimental populations as a function of N applied and to characterize N use efficiency (NUE) as affected by time of N fertilization (experiment one). Experiment tow was conducted to measure glutamine synthetase (GS) activity, leaf ammonium and NUE parameters in eight winter wheat entries at two N levels. Experiment three was a greenhouse experiment conducted to evaluate the effect of continuous N fertilization on soil pH and the relationship between continuous cation removal in forage with soil pH and exchangeable cations.;Findings and conclusions. In experiment one, increasing applied N increased forage, grain and straw yield and N uptake, and N loss. Avoiding excess N application could reduce N losses and hence increase NUE in winter wheat varieties. Estimates of plant N loss from anthesis to fourteen days post-anthesis were greater than those found from fourteen days post-anthesis to maturity. Entries with a high harvest index and low forage yield had low plant N loss. Decreased N loss with split application of N was beneficial in increasing NUE. In experiment two, no entry differences in GS activity, leaf NH...