Nitrogen Requirements of Winter Wheat ( Triticum aestivum , L.) Varieties ‘Blueboy’ and ‘Redcoat’ 1

In 1970–71, five N‐rate field experiments were conducted with fall‐seeded soft red winter wheat ( Triticum aestivum, L.) on limestone‐derived soils in Pennsylvania. Varieties ‘Blueboy’ and ‘Redcoat’ were compared at two locations. At three locations, only Blueboy was grown. Redcoat is widely grown in Pennsylvania, but Blueboy was only recently introduced. The relative nitrogen requirements of these varieties, therefore, was essentially unknown when these studies were begun. Fall and spring applications of 0, 34, 67, 101, 135, and 168 kg/ha of N as ammonium sulfate were compared at each location. The nitrogen content of grain plus straw associated with maximum attainable yield of dry matter was similar among locations and varieties, the mean percent N and its standard deviation being 1.38 ± 0.06%. Yields of grain invariably were depressed when nitrogen in grain plus straw exceeded the mean value of 1.22 ± 0.06% (S.D.). The latter value is considered to represent the internal N requirement of the wheat associated with optimum production of grain, and it corresponds to the percent N in grain plus straw associated with 95 to 98% of total dry matter production. Recovery of fertilizer N was significantly greater for spring than for fall applications, although differences were small (means were 56 and 48%, respectively, for all locations). Yields of Blueboy were substantially greater than those of Redcoat at locations where these varieties were compared. Interactions of rate and time of N application on yields of grain and dry matter and N yields were not significant. Total uptake of N required per unit of wheat grain for maximum attainable yield is almost twice that required for corn.