Response of chickpea accessions to row spacing and plant density on a vertisol on the Darling Downs, south-eastern Queensland. 2. Radiation interception and water use

Interception of radiation by chickpea (Cicer arietinum L.), in a year of below-average rainfall, and water use in both wet and dry years, were studied on a deep vertisol soil at Dalby, south-eastern Queensland. Measurements were made on 4 accessions (cv. Tyson, K223, CPI 56287 and CPI 56289) grown at a number of row spacings. Canopies intercepted less than 20% of incident radiation during the first 70 days after sowing (DAS) in the dry year (1980) before radiation interception reached a peak in mid-September (100 DAS) at about 70% interception in 250 mm rows. Above-ground dry matter was linearly related to intercepted radiation to the end of September (119 DAS), giving an efficiency of radiation conversion of 1.4 g DM per MJ of intercepted photosynthetically active radiation. Efficiency of conversion was marginally higher with 125 mm than with 62.5 mm intra-row spacing in rows 250 mm apart. In a wet year (1979), chickpea extracted water from below 1 m depth in the soil profile and used 356 mm water. In the dry year, only 16 1 mm water was used and none was extracted from below 1 m. K223 used water faster than cv. Tyson, and extraction was faster with close than with wide row spacing. Above-ground dry matter was produced at an efficiency of 3.4 (1980) to 4.2 (1979) g m-2 mm-I of water during the main period of growth through September, and a mean of 0.7 g m-2 seed for 2 seasons was produced per mm of water used over the whole season. The small differences in water extraction between accessions and spacing treatments were reflected during pod-filling as differences in plant water potential of 0.1-0.2 MPa during the early afternoon stress period. Chickpea appears to have poor stomata1 control over water loss, being comparable to summer legumes like soybean rather than to cowpea. We conclude that the benefit of close row spacing in enhancing radiation interception outweighs the small disadvantage from accelerated water depletion. The ability of chickpea to produce useful seed yields over a wide range of soil water availability makes it well suited for opportunistic winter cropping.