Nitrogen inputs from a pasture legume in rotations with cereals in the semi-arid tropics of northern Australia: Experimentation and modelling on a clay loam soil

Two experiments on a Tippera clay loam soil (alfisol) at Katherine, Northern Territory, investigated the nitrogen (N) benefit from legume pasture leys of Caribbean style (Stylosanthes hamata cv. Verano) to subsequent maize crops. Nitrogen uptake and yield of the maize crops were higher after the Verano leys than after a grass ley, the effect persisting into the second crop. The 1-year Verano ley was estimated to have increased N uptake by the maize crops by about 30 kg/ha, and the 3-year ley by about 55 kg/ha over that for the grass. Removing some of the Verano dry matter (DM) as hay at the end of each growing season reduced the subsequent benefit compared with treatments where the Verano DM was rotovated into the surface soil at the end of each growing season, or left standing. However, in all legume treatments, the additional N contributed by the legume was inadequate to fully meet the N requirement of the following crop. The main features of the experimental results, through both the ley and cropping phases, could be simulated adequately using the cropping system model APSIM. The model provided the opportunity to explore the fate of N in the system, and gave insights into aspects of system performance that could not be obtained from the experimental data.