The nitrogen economy of winter wheat

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Abstract
SUMMARY: In a field experiment with 47 wheat genotypes, plant samples were taken at anthesis and maturity and analysed for nitrogen. Taking means over all genotypes, the plants contained at anthesis 83 % of the total present at maturity, while at maturity 68 % of the plant nitrogen was present in the grain.There was significant genetic variation in most of the component attributes determining nitrogen uptake. At anthesis, the heaviest plants contained most nitrogen. Because the nitrogen concentration in the leaves (average 2·8%) was much greater than in the stems and ears (average O8 %) and the leaves comprised, on average, 37 % of the plant weight at anthesis, variation in leanness was the main cause of variation in the nitrogen content of plants of a given weight. During grain filling, plants which lost the most dry weight from their stems and leaves took up the least nitrogen.It is suggested that the strong positive correlation between the accumulation of dry matter and of nitrogen, both until anthesis and during grain filling, occurred because both carbon assimilation and nitrate reduction depend on energy made available from chloroplasts. In addition, assimilate is required to sustain the growth of roots which is necessary for continued nitrate uptake.The results show that it should be easier for breeders to select for high nitrogen uptake from among heavy than from among light genotypes. However, although dwarf genotypes tended to be light, none of the correlations found was strong enough to render it impossible to produce dwarf genotypes capable of giving high yields of high-protein grain.