GROWTH AND YIELD RESPONSE OF BARLEY AND CHICKPEA TO WATER-STRESS UNDER 3 ENVIRONMENTS IN SOUTHEAST QUEENSLAND .1. LIGHT INTERCEPTION, CROP GROWTH AND GRAIN-YIELD

Two barley cultivars (early-maturing Corvette and late-maturing Triumph) and one cultivar of chickpea (Amethyst at Redland Bay and Borwen at Hermitage), were grown in well-watered and water stress trials in three experiments to determine how the effect of water stress on growth and yield of these crops was modified by other environmental conditions, particularly temperature. Two experiments (experiments 1 and 2) were conducted at one location (Redland Bay) with two times of sowing (April and July), while experiment 3 (June sowing) was conducted at Hermitage Research Station, which had much lower temperatures in winter. In water stress trials, rainout shelters were used to exclude rain from plots from crop establishment to approximately maturity. In both well-watered and water stress conditions. the barley crop produced a lower yield when sown in April than in mid-winter, as grain filling occurred in late winter/early spring, when radiation and temperature were low. Chickpea in the irrigated control, however, produced the lowest yield in the July sowing at Redland Bay, because of the rapid increase in temperature in spring which hastened maturity. In water stress trials chickpea produced the lowest yield at Hermitage, as water stress severely reduced crop growth after flowering. Early-maturing Corvette produced a higher grain yield than late-maturing Triumph in one water stress trial (experiment 1), when difference in maturity time was 40 days, but not in others when the difference in maturity was less than 15 days. In most crops, development of water stress was slow during early stages of growth, and severe stress developed after maximum light interception was achieved. In these cases, water stress had a small effect on light interception but a large effect on light use efficiency (total dry matter produced per unit of solar radiation intercepted). However, for the chickpea sown in April, water stress developed during leaf area expansion, and severely reduced light interception with little adverse effect on light use efficiency. The results thus suggest that whether water stress affects light interception or light use efficiency depends on the timing of water stress in relation to the canopy development.