THE IMPACT OF TRASH MANAGEMENT ON SUGARCANE PRODUCTION AND NITROGEN MANAGEMENT: A SIMULATION STUDY

TRASH blankets contain substantial amounts of nitrogen (N) and other nutrients. The availability of N in trash is complicated because most of the N cycles through the soil organic matter. To gain insights into the impacts of trash management on sugarcane production and the long-term fate of N contained in trash, a simulation study was conducted with the APSIM-Sugarcane cropping systems model. Simulations were conducted over 100 years for three different soil types combined with climatic data from five locations from Bundaberg to Tully. Trash management (burnt and GCTB) and N fertiliser application rates (ranging from 0 to 300 kg/ha) were varied in the simulations. The simulation study showed that sugarcane yields have potential to respond positively to trash retention in the range of environments considered. However, achieving these higher potential yields will require that N applications not be reduced following the switch from a burnt to GCTB system. This study also illustrates the potential negative, short-term impact of trash blanketing on sugarcane yields due to the immobilisation of N by the decomposing trash. After at least 5 years, the system comes into a new equilibrium with sufficient N supply in the soil-crop system to allow the trash to decompose without creating N deficits. Implications of this period of disequilibrium on the results of short-term trash management trials and the transition from burnt to GCTB systems are discussed. The results of the simulations also indicate that average environmental losses of N are likely to be greater from GCTB systems at all rates of N fertiliser applications and that particular care should be exercised to avoid over-application of N in GCTB systems.