GROWTH AND GRAIN-YIELD OF CONTRASTING BARLEY CULTIVARS UNDER DIFFERENT PLANT DENSITIES

The effect of planting density on dry-matter growth and grain-yield of contrasting cultivars of barley was examined over three years. The particular objective was to examine whether high-density planting or the use of vigorous cultivars would be disadvantageous in areas where frequent rainfall during early growth is followed by prolonged drought up to maturity. Pre-heading growth varied greatly among cultivars and densities; this variation was partly related to the number of tillers, with two-row cultivars and high densities having more tillers per unit area than six-rows and low densities respectively. The relationship between tiller number and canopy light interception, however, varied among cultivars. A detailed study of two contrasting cultivars showed that the cultivar which had the highest light interception per unit leaf area also had the highest dry-matter production. The result indicates the importance of radiation interception in pre-heading stages with incomplete ground cover. High densities promoted phenological development, with flag-leaf exsertion and heading occurring 6-7 days earlier in the high density (120 plants m-2) than in the low (36 plants m-2). No significant effect of density on grain-yield was observed in one season where water stress developed in the early-grain-filling period. Cultivars which headed earlier tended to escape water stress and produced higher grain-yield. Post-heading growth of late-heading cultivars was low, but this was partially compensated for by the apparent use of pre-heading assimilates. When there was frequent rain during the early stages of growth, water use was not affected by density and cultivar despite a large variation in total dry-matter production among treatments. In another season where favourable weather conditions were maintained throughout growth, yield response to plant density varied among cultivars. In one six-row cultivar with a limited ability to produce tillers, grain-yield increased with increase in density up to the highest of 150 plants m-2. In other cultivars, there was no consistent effect of plant density on grain-yield. It is concluded that grain-yield will not be reduced by the use of high plant density or vigorous cultivars which promote biomass production during early stages of growth, if rainfall is frequent at that time. © 1990.