GROUNDWATER-MANAGEMENT THROUGH INCREASED WATER-USE BY LUPIN CROPS

Total evaporation (E) was measured on lupin crops of differing leaf area per unit ground area in southwestern Australia. Leaf area was controlled by sowing at different times and rates. The objective was to explore the feasibility of increasing water use in order to reduce recharge to rising, shallow, saline water tables. Replicated plots of Lupinus angustifolius were sown at 100 and 200 kg ha-1 on 24 May and at 100 kg ha-1 on 7 June, 1988. E was measured by ventilated chambers from each of these treatments over eight 24 h periods grouped at the beginning, middle and end of a 28 day period. Mean rates of E were 2.16 mm day-1 for the later sown lupins at 100 kg ha-1, 2.49 mm day-1 for the earlier sown lupins at 100 kg ha-1 and 2.90 mm day-1 for the earlier sown lupins at 200 kg ha-1. The corresponding relative values for E were 1.00, 1.15 and 1.34. The transpiration component of E was estimated by measuring sap flow with a heat balance technique on individual plants within the chambers. Daily values of transpiration varied from 0.8 to 2 mm giving residual soil evaporation values of 1.0-1.6 mm day-1. E from soil was a significant cause of water loss particularly in the plots with low leaf area. At preflowering and early flowering E increased linearly with increasing leaf area per unit ground area up to values of 2.6. Soil evaporation decreased linearly with increasing leaf area. We conclude that increased seeding rates and earlier sowing of lupins have the potential to increase E and to reduce recharge and the rise of saline water tables.