Soil water dynamics, herbage production and water use efficiency of three tropical grasses: Implications for use in a variable summer-dominant rainfall environment, Australia

In the moist mid-latitudes of eastern Australia, soil water dynamics, herbage production and water use efficiency (WUE) were monitored during 2006-2008, for five perennial pastures: digit grass (Digitaria eriantha), Rhodes grass (Chloris gayana), forest bluegrass (Bothriochloa bladhii), native grass (Bothriochloa macra and Rytidosperma bipartita dominant), lucerne (Medicago sativa); and two forage crops: oat (Avena fatua) and sorghum (Sorghum bicolor). Ground cover formed more quickly in Rhodes grass and lucerne (>70% ground cover in 120 and 175 days after sowing [DAS] respectively) than in forest bluegrass and digit grass (245 and 365 DAS respectively). Values of maximum extractable water (MEW) for Rhodes grass and lucerne were similar (180-242 mm), while values for digit grass and forest bluegrass (129-175 mm) were equal to or greater than those for native grass, and two annual forage crops (77-144 mm). Lucerne expressed the maximum root depth (1.46 m), while values for the tropical grasses (0.96-1.39 m) were greater than native grasses and forage crops (0.87-0.96 m). Native grasses (6.5-12 t DM/ha) had the lowest herbage production, which resulted in values of WUE that were significantly less than most other treatments (16-21 vs. 23-43 kg DM ha(-1) mm(-1)). Digit grass (33-34 kg DM ha(-1) mm(-1)) had higher WUE compared with the other tropical grasses (20-27 kg DM ha(-1) mm(-1)). The data collected here suggest that a forage system comprising digit grass, lucerne and forage oat would provide high production and WUE in this environment.