Net primary productivity and rainfall use efficiency of pastures on reconstructed land following open-cut coal mining in central Queensland, Australia

The development of improved pastures for cattle grazing is a logical post-mining land-use option for the Bowen Basin coalfields of central Queensland, but little is known of the potential productivity or livestock carrying capacity of these systems. A research program was instigated to determine key indicators of grazing capacity, viz. above-ground net primary productivity (NPP) and rainfall use efficiency (RUE), at 18 plots across 3 mines. NPP ranged from 3000-11 000 kg/ha/yr and RUE ranged from 4-21 kg/ha/mm. These results are comparable with those for buffel grass pastures on unmined lands in the region. Multivariate linear regression was used to develop a model for prediction of RUE from plot topographic and edaphic characteristics. The variables of slope, magnesium concentration and exchangeable sodium percentage most effectively predicted RUE (cumulative r(2) = 0.77). Predicted RUE and average seasonal rainfall were then used to predict NPP for the 3 mines. Safe stocking rates were calculated based on 30% utilisation of seasonal NPP.