Sowing date and nitrogen input influence nitrogen-use efficiency in spring bread and durum wheat genotypes

Environmental and economic considerations require the effective use of nitrogen (N) fertilizer in wheat production. This study evaluated genetic variation in nitrogen-use efficiency (NUE) for grain yield (NUEY) and protein (NUEP), and their components using nine bread wheat (Triticum aestivum L.) genotypes, five durum wheat (T. turgidum, var. durum Desf.) genotypes and a triticale (x Triticosecale Wittmak) genotype under 105 (N1) and 170 (N2) kg N ha(-1) sown in October (early) December (optimum), and February (late) 1993 at the Moreno Valley Field Station of University of California, Riverside. Late and early sowing decreased mean grain yield and harvest index, respectively. Mean NUEY and NUEP was greater at optimum and early than at late sowing, but their components, N-uptake efficiency, N-production efficiency, and N-partitioning efficiency exhibited different patterns. Greater N supply, on average, increased shoot biomass by 29%, grain yield by 16%, and percent protein by 5%, but decreased harvest index by 10%, NUEY by 28%, NUEP by 26%, N-uptake efficiency by 18%, N-production efficiency by 12%, and N-partitioning efficiency by 8%. However, genotypes responded differently to sowing date and N rate for different characters. None of the genotypes examined consistently performed satisfactorily over different sowing dates and all, but one at early sowing, had similar or reduced NUEY and NUEP at N2 than at N1. Genotypic variation in modern bread and durum wheat was relatively small for NUEY and NUEP. Nitrogen-uptake efficiency was the most important component of both NUEY and NUEP. Correlation coefficients between NUEY and NUEP ranged from 0.83 to 0.98, whereas those between the components were nonsignificant in all cases, except one. Selection for N-uptake efficiency under low N input should improve both NUEY and NUEP in wheat. Wheat genotypes with desirable characteristics under low N input were identified for early, optimum, and late sowing.