INTERACTIVE EFFECTS OF WATER AND NITROGEN STRESSES ON NITROGEN-UTILIZATION EFFICIENCY, LEAF WATER STATUS AND YIELD OF CORN GENOTYPES

Information on the combined effects of N and water stresses on com (Zea mays L.) is of importance for selecting nitrogen efficient and drought tolerant genotypes. Greenhouse and field experiments were conducted to determine the interactive effects of N and water stresses on N utilization efficiency (NUE), leaf water status and yield of diverse com genotypes. Three genotypes which normally rank differently for NUE in the field, were grown to the 9-leaf stage in the greenhouse with four N rates of 0, 30, 60, and 90 mg/kg and two water regimes (stressed for 8-d, and unstressed). In the field experiment, four genotypes with different NUE history, were grown with N rates of 0, 60, 120, and 180 kg/ha, and water regimes of irrigated and dryland. Maximum grain yield was obtained at different N rates for different genotypes and for different water regimes. The genotypes differed significantly in NUE as expected, but also for water use efficiency (WUE) in both experiments. Nitrogen x water regime interactions for NUE were not significant in either experiment. Water regime did not significantly change the rank among genotypes for NUE as the genotype x water regime interactions for NUE were not significant in either of the two environments. This should greatly simplify selection of com genotypes for NUE. NUE paralleled WUE closely for the genotypes studied. There was 19% difference between the best and poorest nitrogen efficient hybrids in terms of grain produced per kg total N uptake. Increasing N rate further decreased the-total water potential of water stressed plants. There was a significant N x water regime interaction for grain yield. The grain yield increases due to irrigation compared to dryland ranged from 23% to 84% for the genotypes studied. Leaf water and osmotic potentials decreased significantly as N rate increased in the dryland, but were the same over N rates in irrigated plants. Apparent remobilization of N from leaves to grain was the major source of grain N in all genotypes, however, there were differences between genotypes for the fraction of leaf N remobilized. Genotypic selection for NUE does not appear to be influenced by water regime, and may result in simultaneous selection for WUE.