No-till seeded winter wheat: influence or date of nitrogen application on the grain yield, grain protein, and yield components
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An experiment was carried out to determine the influence of date of nitrogen (N) fertilizer application on the grain yield, quality, and water use efficiency (WUE) for dry matter and grain yield production of no-till seeded winter wheat. Ammonium nitrate N was surface broadcast either as early as possible in the spring (early), split between 2/3 early and 113 at the beginning of stem elongation (split), and 3 weeks after early (late), at rates of 0,34,67,101,134,167, and 202 kg N ha-1. Grain yields ranged from 0.25 to 2.5 t ha-1. High pre-anthesis evaporative demand in 1988 reduced mean grain yield to 0.89 t ha-1 (42 % of 1987 yields). While 3 of the 8 trials showed a positive response to N rate, date of N application had no effect on harvest yield and yield components. Grain protein yield and protein concentration were better indicators of N response under these high stress conditions with 6 and 7, respectively, of the 8 trials showing a positive response to N rate. Added N increased water use efficiency of dry matter and grain yield in 5 and 3 of the trials, respectively. Increases in WUE were a reflection of grain and dry matter yield responses to added N and not differences in season long ET. The threshold ET required for zero dry matter and grain yield was 46 and 77 mm, respectively. Forward step-wise regression identified pre-anthesis evaporative demand as the only environmental or soil water parameter influencing harvest dry matter and grain yield response. Dependence of crop response on pre-anthesis evaporation indicates that yield was a function of the atmospheric demand for water in this experiment. Kernels per spike was the yield component that best represented grain yield, explaining 82 % of the variation recorded. High evaporative demand during stem elongation reduced the survival of early established tillers and increased the role of kernels per spike, the other pre-anthesis determined yield component, in grain yield formation. Only with the unfertilized check, where pre-anthesis production was reduced due to N deficiencies, did kernel weight have any significant influence in determining grain yield.
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