MODELLING SUGARCANE YIELD RESPONSE TO APPLIED NITROGEN FERTILISER IN A WET TROPICAL ENVIRONMENT

THE CAPABILITY OF the APSIM-Sugarcane model to simulate N management in the sugarcane farming system is well demonstrated for most Australian production areas. In particular, the APSIM-Sugarcane model has been used to investigate the impact of trash management on sugarcane yields and N dynamics, N leaching below the root zone and management options to reduce N losses and improve N fertiliser use efficiency. We used APSIM to gain a preliminary insight into the impact of natural climate variability on the N fertiliser requirements of sugarcane. APSIM was calibrated against a smallplot, N-rate field trial conducted at BSES Tully from 2004 to 2009. Next, the optimum amount of N required for each year of the trial that would produce 95% of the maximum yield along with the grower and industry economic returns were calculated from the simulated and observed response curves for comparison to the recommended N rate for the site as determined by the SIX EASY STEPS N-management guidelines. Although the APSIM model provided indicative estimated sugarcane yields using the Tully trial data, problems were encountered with waterlogged conditions and when N rates were varied. The SIX EASY STEPS N guidelines did not grossly underestimate or overestimate N requirements compared to the optimal N rate for each year. However, fine tuning will improve the ability of this system to adapt to annual yield fluctuations caused by natural climatic variability. Options that may improve the ability of this system to better match N fertiliser inputs to crop requirements have been identified.