Phenology, seed yield and water use of grain legumes grown under different soil water regimes in a semi-arid tropical environment

Abstract

The comparative responses of phenology, and seed yield and its components to prolonged water deficits in soybean ( Glycine max cvs. Buchanan and Durack), green gram ( Vigna radiata cvs. Berken and CES-ID 21), black gram ( V. mungo cv. Regur), cowpea ( V. unguiculata cv. Red Caloona), labaab bean ( Lablab purpureus cv. Highworth) and pigeon pea ( Cajanus cajan cvs. Royes and insensitive ICP7179) was examined during the dry season in semi-arid tropical Australia. In general, water deficits had little effect on the date of flowering, but the duration of flowering and pod-filling was reduced and the time to maturity was markedly shortened. Under well-watered conditions, seed yields were similar in green gram, cowpea, soybean and pigeon pea, with slightly higher yields being obtained in black gram and lablab bean. In contrast, green gram, cowpea and lablab bean produced the highest yield under conditions of water deficit. Early-maturing cultivars yielded better than late-maturing cultivars but inter-species variation in seed yield was not necessarily related to phenology. Most of the reduction in yield arose from a decrease in pod numbers although there was some variation in seed size and seeds per pod. In contrast to absolute yield levels, the reduction in yield due to water deficits relative to the well-watered situation was, with the exception of black graam, greater the later the maturity of the grain legume. Thus the relative reduction in yield was least in green gram, followed by cowpea, soybean cv. Buchanan, insensitive pigeon pea, and lablab bean, with black gram, soybean cv. Durack and pigeon pea cv. Royes having the greatest yield reduction due to water deficits. Variation in productivity was also examined in terms of evapotranspiration (ET) and water use efficiency (WUE DM on a net above-ground dry matter basis, and WUE y on a seed yield basis). Under prolonged water deficits, lablab bean, soybean cv. Durack and both pigeon-pea cultivars extracted the most water. These differences in ET were examined in terms of rooting characteristics. WUE DM was unaffected by water deficits in both soybean cultivars, both green grams and cowpea, but tended to decrease in response to water deficits in the remaining grain legumes. WUE y was more responsive to water deficits than WUE DM. Only in the early-maturing green grams and cowpea was WUE y unaffected by water deficits.