Utilization of late-applied fertilizer nitrogen by spring wheat genotypes

Abstract

To attain acceptable grain protein concentrations with high yielding wheat varieties, N uptake after flowering is desirable. The study examined genotypic differences in the utilization of lateapplied N fertilizer by wheat. Four spring wheat genotypes, grown at three early N levels (40, 90, 140 kg N ha−1 applied before EC 23) were supplied with 0, 50, 100 kg N ha−1 at heading. Nitrogen in the crop at maturity was related to above-ground biomass, grain yield, senescence and residual mineral N contents in the soil (0–100 cm depth). Nitrogen in the crop at maturity increased up to the highest late N level. At the lower early N levels, late infertile tiller production influenced the genotype-specific utilization of late applied N, predominantly by decreasing the N present in the fertile shoots. At the highest early N level (N140), which was not affected by late tillering, utilization of late-applied N was similar for each genotype, although the genotypes differed in above-ground biomass and senescence. At N140, apparent utilization of the late N applications was 64 (50 kg N ha–1 applied) and 55 (100 kg N ha−1 applied) per cent. Because residual mineral N contents in the soil at maturity showed no significant difference between the late N levels at N140, the poor fertilizer N utilization could not be ascribed to physiological restrictions, but was apparently due to losses of plant-available N caused e.g. by leaching, denitrification, or volatilization from the crop or microbial immobilization. Nitrogen harvest index was not reduced by late N applications. The results show that investigations on genotypic variation in late N uptake require accompanying examinations of the soil mineral N status.