Evaluation of strategies for increasing irrigation water productivity of maize in southern New South Wales using the MaizeMan model

MaizeMan is Windows-based decision support software, derived from CERES Maize and SWAGMAN Destiny, which can be used for real-time irrigation scheduling or strategic analysis. Evaluation of MaizeMan for sprinkler and furrow-irrigated maize (Pioneer 3153) showed good predictive ability for yield, biomass, runoff and soil water depletion between sowing and harvest. MaizeMan simulations using 43 years of weather data from Griffith, New South Wales, suggested that the biggest influence on yield, irrigation requirement and irrigation water productivity is seasonal weather conditions. For example, yield of October-sown 3153 irrigated frequently to avoid soil water deficit varied from about 8 to 16 t/ha, while net irrigation and net irrigation water productivity varied from 7 to 11 ML/ha and 0.8 to 1.6 t/ML, respectively. The optimum sowing window for maximising yield and irrigation water productivity is wide, from late September to mid November. Delaying sowing beyond this may result in higher yield and irrigation water productivity; however, delayed maturity would lead to problems for grain drying and harvesting in winter and increased insect pressure. The simplest management strategy for maximising yield and irrigation water productivity is irrigation scheduling tailored to soil type. Irrigation scheduling can be assisted by real-time scheduling using MaizeMan, provided soil hydraulic properties are accurately characterised. One to two irrigations can also be saved by growing shorter duration hybrids, but the tradeoff is lower yield, while irrigation water productivity is maintained. Simulated sprinkler irrigation increased yield and net irrigation water productivity by small amounts (averages of 0.5 t/ha and 0.2 t/ML, respectively) relative to well-scheduled flood irrigation, through improved soil water and aeration status and reduced deep drainage loss.