| Abstract: | Secondary salinisation of soil and water resources is an acute management issue over large parts of Australia. This paper focusses on the situation in the Liverpool Plains, where secondary soil salinity is on the increase due to rising saline groundwater tables. The Liverpool Plains are famous for the vast alluvial floodplains where self-mulching black clays provide the production basis for an extensive dryland cropping industry. The farmers there are asking how best to manage their resources under the present hydrological conditions, and are concerned whether their businesses will remain viable in the future. A multi-period programming model is applied to a model farm situation. The objective function reflects the economic paradigm of farming. The model includes a simulation sub-routine which links land use, rainfall and lateral groundwater flow into a point water balance and estimates the salt-affected area. A feedback relationship applies between soil salinity and land productivity. The results of the model suggest that the prevailing cropping practices that rely on long fallowing for soil moisture retention are sub-optimal. Increased cropping frequency increases farm income and reduces on-farm recharge to groundwater. Diversification into lucerne is favourable for the same reasons. Unless trees have commercial value, tree planting is not a favoured option except on salt-affected land. The farm achieves complete on-farm recharge control. However, assuming that the groundwater table rises at a rate of 10 cm per year independent of on-farm recharge, salinisation continues despite these land management changes. The subsequent land productivity losses render the model farm financially unviable in the medium term. Sustaining the productivity of the Liverpool Plains is an issue of reducing recharge to the groundwater system by changing land-use practices throughout the entire catchment. © 1997 John Wiley & Sons, Ltd. |
