SIMULATION OF A LEGUME LEY FARMING SYSTEM IN NORTHERN AUSTRALIA USINGTHE AGRICULTURAL-PRODUCTION-SYSTEMS-SIMULATOR

An innovative ley farming system, involving cereal crops, grown in rot ation with pasture legumes, has been tentatively adopted by farmers in the semi-arid tropics of northern Australia. Yet, after more than a d ecade of experimental research, the long-term potential of this system remains uncertain. The approach used to address this question has bee n to use the APSIM (Agricultural Production Systems Simulator) model i n conjunction with historical climate records to simulate system perfo rmance. Thus, the objectives of this paper were to describe APSIM, to test its performance against data from cropping systems experiments, a nd to use it in assessing the long-term consequences of alternative fa rming practice in this region of northern Australia. APSIM is able to simulate the soil carbon, water and nitrogen balances arising from int eractions between different crops and pastures grown in rotation. In t his paper, APSIM was configured to simulate either conventional rotati ons of sorghum or maize crops, or crops grown in rotation with Stylosa nthes hamata (Verano) ley pastures. In the latter case, APSIM simulate s the establishment of a Verano pasture sward, its growth and death, a nd its effects on subsequent cereal crops. The crop is either kept fre e of weeds or, alternatively, an understorey of volunteer legume can e stablish to form an intercrop where the crop and pasture compete for r esources. Simulation of crop and pasture residues can encompass either their retention on the soil surface and decomposition over time, or t heir complete removal from the system (as hay). In comparisons of simu lations against limited experimental data, APSIM was able to reproduce the measured yields from sorghum, maize and Verano grown either as so le crops, as intercrops, or in rotations of several years. Likewise, a simulation analysis using APSIM of several cropping options for Kathe rine, Northern Territory, resulted in the preferred outcome reflecting current farming practices in the region. This preferred option, a com bination of legume hay and sorghum grain production, was shown to be s uperior in terms of both gross margin returns and long-term soil ferti lity status. It was concluded that APSIM now provides a useful tool wi th which farming systems in northern Australia can be further explored .