Genotypic variation in grain nitrogen content of wheat as affected by mineral nitrogen supply in the soil

Abstract

In wheat, genotypic variability in grain protein content may be affected not only by physiological traits but also by N supply in the soil. The relative importance of these factors was studied for two years, in field experiments with eleven recent spring wheat genotypes and four N regimes. Genotypic differences in grain N content were found only at low early N supply. The extent of genotypic variability in grain N content was generally more strongly related to N uptake than to N translocation. This was ascribed to the high nitrogen harvest index (NHI) of 0.80 to 0.86. Under high early N supply, genotypic variation in N uptake decreased between anthesis and maturity, resulting in non-significant differences in N uptake and, concomitantly, in grain N content at maturity. This feature, also reflected in a negative correlation between pre- and post-floral N uptake, suggests an effect of N supply. Mineral N content in the soil to a depth of 100 cm showed that at flowering and without N application at heading, the soil contained between 22 and 33 kg mineral N per ha. Under each N regime, nitrogen from current N mineralization or from deeper soil layers contributed to post-floral N uptake. It was concluded that the extent of genotypic variation in N uptake and grain N content may be severely restricted by spatial and temporal availability of nitrogen.