Forecasting lucerne productivity under dryland farming conditions in central-western and western New South Wales

Possibilities for growing dryland lucerne (Medicago sativa L.) productively in drier parts of central-western and western New South Wales (NSW) were investigated by consideration of meteorological records. Annual rainfall data and estimated evapotranspiration data for 1995-1999 were compiled to calculate lucerne growing days and N₂-fixing days at Condobolin, Trangie, Cobar and Wentworth. This information was used in conjunction with seasonal indices of dry matter production and nitrogen fixation derived from the work of Bowman et al. [Aust J Exp Agric 42 (2002) 439] at Trangie to estimate yearly biomass production and N₂ fixation for the four locations. It was concluded that (i) there are good prospects for growing lucerne productively on suitable soils located in that extensive region of central-western and western NSW between the 450 and 300 mm isohyets if it is feasible to develop techniques for establishment and management to maintain stands at an acceptable density—not less than eight plants/m², (ii) there are only poor prospects for growing lucerne in those western parts of the state where annual rainfall averages less 300 mm, and (iii) annual rainfall, irrespective of other factors such as erratic distribution, is a rough guide to potential lucerne production. In addition, there were indications that, were the threshold for cessation of lucerne N₂ fixation reduced by 2 °C (say from 10 to 8 °C), annual N₂ fixation would be enhanced by more than 20%.