Determining irrigation requirements and crop yield using a water balance model

Yields of sugarcane were calculated for different irrigation methods, quantities of irrigation water, system delivery capacities, electricity tariffs, soil types and trash management practices, using a water balance model for an economic evaluation of irrigation methods and programs at Bundaberg. Simulated yields agreed closely with district average yields for the same quantity of irrigation water. Effective rainfalls calculated using the daily water balance model were much lower than calculated previously, and varied considerably with soil water holding capacity. The quantity of irrigation water influenced yield more than irrigation method. Of the four irrigation methods compared, drip irrigation generally gave the highest yield. Reduced system capacity such as night-only irrigation increased yield on soils with low water holding capacity, but reduced yields on soils with high water holding capacity. The method used to model the effects of trash blanketing was unsatisfac. tory. This project emphasised the value of models in determining probable outcomes when comparing systems with many variables. The ability to run each scenario for 25 years of daily rainfall and evaporation data produced valuable information on irrigation at Bundaberg.