EFFECTS OF POSTANTHESIS WATER-STRESS ON THE YIELD AND GRAIN PROTEIN-CONCENTRATION OF BARLEY GROWN AT 2 LEVELS OF NITROGEN

The interaction between nitrogen (N) rate and post-anthesis moisture s tress in 6 cultivars of barley (Clipper, Stirling, Weeah, Schooner, Ch ebec, and Skiff) was examined. Plants were grown in a glasshouse at 2 rates of N under well-watered conditions until 3 days after ear emerge nce, when the stress treatment was started. Yield and grain protein co ncentration (GPC) responses and changes in the dry matter and N conten t of the straw and grain in the main stem and tillers were examined se parately. Nitrogen increased grain yield in all cultivars except Weeah , with Skiff and Stirling being the most responsive. Post-anthesis str ess did not reduce yields at the low N rate but large reductions occur red at the high N rate in all cultivars; the yields of Stirling, Chebe c, and Skiff were most affected. At the low N rate, stress did not sig nificantly affect kernel weight and GPC, but kernel weight declined an d GPC increased at the high N rate. Compared with the main stem, tille rs produced smaller grain with a lower GPC. The responses to Nand wate r stress, and the different sensitivities of cultivars to stress, were largely due to the effects of the treatments on the growth of the til lers. In Stirling, Chebec, and Skiff, grain yield and kernel weight fr om the tillers were greatly reduced by stress, whereas Clipper showed relatively little effect of N and stress on yield and kernel weight. N et remobilisation of dry matter was increased by stress but not by N t reatment, and the amount remobilised varied between genotypes. At the high N rate, post-anthesis stress increased the N content per kernel a nd net remobilisation of N. Although genotypes differed in the net amo unt of N remobilised and in the N harvest index, there was little vari ation in GPC between cultivars. The work demonstrated that reductions in yield and kernel weight and increases in GPC from post-anthesis str ess can be greater when plants are grown at a high rate of N than when the supply of N is limited. The different responses to stress and N a mong the 6 cultivars were associated, in part, with the pattern of til ler development. However, there appeared to be differences in the sens itivity of grain filling to stress independent of the responses in tii lering. While the net remobilisation of dry matter and N differed betw een cultivars, the amounts did not appear to be related to differences in kernel weight or GPC.