Application of AGNPS to model nutrient generation rates under different farming management practices at the Gunnedah Research Centre catchment

Abstract

Data collected at a conservation tillage trial site operational between 1971 and 1986 were used to assess the performance of the Agricultural Non-Point Source model (AGNPS). Eight trial plots, each of about 1 ha (average slope of 3.8%), were established on the black earths of paddock 2 at the Gunnedah Research Centre, New South Wales. The plots were subjected in pairs to stubble-burning, stubble incorporation, stubble-mulching, and no-tillage treatments. Runoff and peak flow rate from the plots, resulting from 5 rainfall events between 1982 and 1986, were used to calibrate the hydrology module of AGNPS. Hydrologic simulations for each plot and associated tillage treatment performed after calibration showed that conservation farming practices could effectively reduce runoff and peak flow rate. AGNPS was also used to simulate nutrient generation rates, defined as the transport of soluble and sediment-adsorbed nitrogen and phosphorus in runoff and sediment discharge, for the whole catchment for a number of rainfall events. The model predicted that nutrient movement could be reduced using best management practices, including the implementation of contour banks, contour cultivation, and no tillage. Additional information related to soil chemical properties and pore/surface water nutrient content could improve model performance.