A survey of water use efficiency on irrigated dairy farms in northern Victoria

Water use efficiency (WUE) in irrigated dairy systems has been defined, in this paper, as the amount of milk (kg milk fat plus protein) produced from pasture per megalitre of water (irrigation plus effective rainfall). A farm survey was conducted for the 1997–98 and 1998–99 seasons in the Goulburn Irrigation System (GIS) and Murray Irrigation System (MIS) when the irrigation water allocated to irrigators in the GIS was low (100–120% of water right compared with the MIS which was 130 and 200% of water right). These data were analysed in conjunction with information collected on the same farms in the 1994–95 and 1995–96 seasons when the irrigation water allocated to irrigators in both systems was above 150% of water right (Armstrong et al. 1998, 2000). The aim of the survey was to determine if the management decisions made by dairy farmers in seasons of low irrigation water allocations had an impact on WUE. Milk production averaged across the 2 irrigation systems increased significantly over the 5-year period (57 540–75 040 kg milk fat + protein per farm). Over the same period the amount of irrigation water applied (GIS 7.6 ML/ha, MIS 9.2 ML/ha) and the milking area (GIS 72 ha, MIS 73 ha) remained constant. The amount of concentrates fed per cow (GIS 650–1100 kg DM, MIS 480–860 kg DM) and per farm (GIS 119–228 t DM, MIS 72–157 t DM) increased, but pasture consumption (GIS 8.9–9.5 t DM/ha, MIS 9.1–9.7 t DM/ha) did not increase significantly over the survey period. Therefore, the increase in milk production appeared to come primarily from an increase in supplementary feeding rather than an increase in pasture consumption, resulting in no significant change in WUE in either system (GIS 66 kg milk fat + protein/ML, MIS 61 kg milk fat + protein/ML). The survey results indicate that despite varying water allocations in the 2 major irrigation systems in northern Victoria, milk production on farms in both systems increased while changes in WUE could not be detected by the methods used. This suggests tactical options to increase WUE in response to short-term changes in water allocation were either difficult to implement or not a priority in a business sense.