Nitrogen Stress of Winter Wheat Changed the Determinants of Yield and the Distribution of Nitrogen and Total Dry Matter During Grain Filling

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Abstract
The yields of grain dry matter (DM) and nitrogen (N) of winter wheat (cv. Maris Huntsman) were decreased by 26% and 45% when no fertilizer-N was applied in the spring. Fewer ears per m² and less mass of N per grain were the major reasons for the decreased yields. The low-N treatment decreased the rate and duration of grain filling for N but not for DM. Net assimilation of DM and N by the shoots of the low-N crop ceased at 35 and 28 days after anthesis but both continued, at a declining rate, through to maturity for the high-N crop; rates of grain-filling of DM and N were sustained at a constant rate for 2 weeks more as vegetative DM and N were redistributed. From 28 days to maturity the potential contribution to grain yield of DM and N from mobilized sources was estimated at 65% for both for the high-N crop, and 96% and 87%, respectively, for the low-N crop.