APPLICATION OF AGNPS TO MODEL NUTRIENT GENERATION RATES UNDER DIFFERENT FARMING MANAGEMENT-PRACTICES AT THE GUNNEDAH RESEARCH-CENTER CATCHMENT

Data collected at a conservation tillage trial site operational betwee n 1971 and 1986 were used to assess the performance of the Agricultura l Non-Point Source model (AGNPS). Eight trial plots, each of about 1 h a (average slope of 3.8%), were established on the black earths of pad dock 2 at the Gunnedah Research Centre, New South Wales. The plots wer e subjected in pairs to stubble-burning, stubble incorporation, stubbl e-mulching, and no-tillage treatments. Runoff and peak flow rate from the plots, resulting from 5 rainfall events between 1982 and 1986, wer e used to calibrate the hydrology module of AGNPS. Hydrologic simulati ons for each plot and associated tillage treatment performed after cal ibration showed that conservation farming practices could effectively reduce runoff and peak flow rate. AGNPS was also used to simulate nutr ient generation rates, defined as the transport of soluble and sedimen t-adsorbed nitrogen and phosphorus in runoff and sediment discharge, f or the whole catchment for a number of rainfall events. The model pred icted that nutrient movement could be reduced using best management pr actices, including the implementation of contour banks, contour cultiv ation, and no tillage. Additional information related to soil chemical properties and pore/surface water nutrient content could improve mode l performance.