Recharge estimation for the Liverpool Plains

Dryland salinity is recognised as a major environmental concern on the Liverpool Plains in north-eastern New South Wales. Previous hydrogeological and dryland salinity studies have highlighted the importance of adopting appropriate farming systems to reduce recharge into shallow aquifers. In this study, we applied the cropping systems model PERFECT to investigate the effects of climate, soil, and land use on recharge. Model inputs were derived from a range of sources including historical weather data, soil survey data, and information from landholder surveys. We investigated 47 different soils identified in a published soil survey covering approximately 280 000 ha of the Liverpool Plains. This study demonstrated a significant variation in soil physical properties and estimated recharge within soil types and illustrates the dangers of generalising soils into broad groupings. For example, under a wheat-sorghum rotation, predicted average annual recharge for soils classified as black earths ranged from 28 to 80 mm. Similar variability of predicted drainage is evident within other Great Soil Groups. The results reveal that response cropping alone will not significantly reduce recharge for all soils. Considering one black earth soil, average annual recharge is predicted to be 48 mm for a wheat-sorghum rotation, 22 mm for a response cropping rotation, and 8 mm for a lucerne-response cropping rotation. Therefore, including lucerne within a response cropping system is of benefit in reducing recharge. For all soil types, least recharge is predicted for permanent pasture but this land use is not an attractive option to farmers given the diversity of farming systems in the region. However, for some soils, continuous pasture is appropriate because excessive recharge is estimated for all cropping systems. This study has extended previous modelling work in the region as it considered a much wider range of soil types and cropping systems than previously investigated. Such a modelling approach permits the quantification of the effects of climate, soil type, and land use on recharge below the root-zone.