NITROGEN PARTITIONING IN GENOTYPES OF WINTER-WHEAT DIFFERING IN GRAIN N-CONCENTRATION

A three-year field study was conducted to establish the relationship between grain yield, grain N concentration (gnc), post-anthesis N uptake, and nitrogen harvest index in winter wheat (Triticum aestivum L.) genotypes varying in gnc. Yield was negatively associated with gnc but correlation between the two was only moderate (-0.43 to -0.60*). Genotypes differed in flag leaf nitrate reductase activities (nra), but nra was not correlated with gnc, total grain N, or yield. Nitrogen harvest index, which ranged from 0.55 to 0.78, was not correlated with gnc or yield. Redistribution of vegetative N contributed significantly more to grain N than post-anthesis N uptake, which generally accounted for less than 10% of the total N at maturity. The range of post-anthesis N-uptake values among genotypes was also small and not significantly different between genotypes. Vegetative N at maturity increased as a result of supplemental N applied at anthesis, but gnc, total grain N, and yield were unaffected. Apparently, the additional N was not easily partitioned to the grain. Since nitrogen harvest index and other N-redistribution variables were not correlated with gnc, improvement in gnc may require an improvement in both post-anthesis N uptake and increased partitioning of that N to the grain. © 1990.