Responsiveness of Wheat Cultivars to Nitrogen Fertilizer
Genotypic differences in responses to nitrogen (N) fertilizer of 6 cultivar of wheat (Atrak, Falat, Fong, Star, Showa, Atila) grown at 6 different rates of N (0, 50, 00, 50, 200 and 250 kg N ha-1) were examined. Measurements of vegetative growth, N content, grain yield (GY), grain protein concentration (GPC) and yield components were taken to identify traits that may contribute to high yield responsiveness. The optimum rates of N for dry matter production at ear emergance (DMee) were greater than 80 kg N ha-1 for all cultivar and often growth increased up to 105 kg N ha-1. Optimum rates of N for grain yield (Nopt) were lower and ranged, on average, from 50 kg N ha-1 for Clipper to 96 kg N ha-1 for Showa. The initial response to N varied from 13-14 kg kg-1 N in Showa, Fong and Star, to 36 kg kg-1 N in Atila. The Nopt for Atila was 71 kg N ha-1 and it tended to show the greatest yield response to N. It produced 19 kernels/g DMee, compared with 15-17 kernels/g DMee in the other cultivars. Unlike most other cultivars, Atila`s yield was consistently and positively correlated with ears m2, Falat was the only cultivar to show a similar relationship. However, the average kernel weight of Atlia was up to 5 mg lower than that of Atrak, Fong and Star and varied more than these cultivars between sites, suggesting that consistent grain size may be a problem in this cultivar. Atrak and Star had lower Nopt (51 kg ha-1) and a less variable kernel weight. There were no signs of differences in GPC of the 6 cultivars used at 3 N-responsive sites. Adding N increased GPC up to the highest rate of N and the responses were generally linear. Average N rates of between 38 kg N ha-1 (Star) and 58 kg N ha-1 (Atila) were sufficient to raise GPC above 11.8%. The experiments showed that the N rates for optimum yields varied considerably among cultivars, but applying rates to achieve maximum yields may cause GPC to exceed the maximum value.
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