The Brigalow catchment study: More than 20 years of monitoring water balance and soil fertility of brigalow lands after clearing for cropping or pasture

The Brigalow Catchment Study was established to determine the impact on hydrology and soil fertility when brigalow land is cleared for cropping or pasture. This paired catchment study commenced in 1965, when three catchments were selected in central Queensland, Australia, to represent the extensive brigalow bioregion of approximately 40 million hectares. Catchment hydrology was characterised during a 17-year calibration period (1965–81). In 1982, two of the three catchments were cleared, with one developed for cropping and the other sown to improved pasture. The third catchment was retained as an uncleared control. Soil sampling on 13 occasions from 1981-2007 allowed changes in soil fertility to be characterised. Land development for either cropping or grazing has doubled runoff and increased peak runoff rates. Deep drainage increased dramatically during land development and significant amounts of soil chloride were leached. This continues to occur under cropping. Cropping has resulted in a decline in soil organic carbon, total nitrogen and bicarbonate-extractable phosphorus. Grazing beef cattle on improved pasture however has maintained soil organic carbon and total nitrogen levels, but has shown a greater decline in bicarbonateextractable phosphorus than cropping.