On-farm measurement of the water use and productivity of maize

Abstract

Maize, as a C4 species, is likely to use water more productively than the perennial ryegrass and white clover pastures typically grown for dairy cows in northern Victoria. However, only estimates of water use by irrigated maize crops are available for this region. We measured the growth and water use of three commercial maize crops used for silage in northern Victoria. Crops under centre pivot irrigation were monitored in 2003–04 (Spray 1) and 2004–05 (Spray 2). A border-check irrigated crop (Border-check) was monitored in 2004–05. The Spray 1 crop was irrigated 30 times and received 782 mm of rainfall and irrigation. The crop yielded 22 t DM/ha, giving a water productivity of 28 kg DM/ha.mm (including irrigation, rainfall and change in soil water content). In the cooler, wetter summer of 2004–05, the water productivity was 34 kg DM/ha.mm for the Spray 2 crop and 30 kg DM/ha.mm for the Border-check crop. Crop evapotranspiration was estimated from weather data and a daily soil water balance was computed according to FAO 56. The estimated and measured changes in soil water content were in good agreement and indicated that the basal crop coefficients in the model (Kcb = 1.15 during the mid-season, before correction for non-standard humidity and wind speed) were appropriate to local conditions. Maize grown for silage in northern Victoria has higher water productivity than pastures. However, high yields are required to make it economically viable compared with alternative forages for dairy cows. These data will assist dairy farmers to select the optimum forage mix for their enterprises.