Variation in the effectiveness of rainfall meeting crop water requirements in the Australian sugar industry

Efficient management of water on-farm is vital to the sustainability of the Anslralian sugar industry. Knowledge of Ihe effectiveness of rainfall in different seasons. locations and prodnction systems allows hener definition of the irrigation requirement and the scope for more efficiem water managemem practices. Th!S srudy used the APSIM-Sugarcaue model and historical climate data to assess the variation in effect! ve raInfall defined as that fraction of tbe total rainfall available to grow the crop. Effective rainfall was highly variable across years, locations and between irrigated and rainfed systems. Effect!ve raInfall was less variable across soil types and crop start dares. The analysIs showed that effective rainfall cannot be assnmed to be a constant percentage of total rainfall, as has been suggested previously. This paper gives gn!deHnes for those factors in the sugarcane production system that should be taken account of when calculating effective rainfall.