Limited application of irrigation water does not affect the nutritive characteristics of lucerne

Lucerne (Medicago sativa) has not been a significant part of the feedbase of the Murray-Dairy Region of Australia. However, under future climate regimes, which are indicating an overall decline in rainfall as well as water available for irrigation of pastures, lucerne is emerging as a potential forage species because of its adaptability, productivity and resilience. A large-scale field experiment was conducted at Tatura, Victoria, Australia, over four years to determine the dry matter (DM) production and nutritive characteristics of lucerne under a range of limiting and non-limiting irrigation management practices. Nine irrigation treatments were imposed that ranged from full irrigation to no irrigation in either a single, or over consecutive, irrigation seasons. Plots were harvested using plant-based criteria over the irrigation season and DM production and nutritive characteristics were determined. DM production generally increased as the total water supply (irrigation plus rainfall plus changes in soil water) increased, with the fully irrigated treatments producing significantly more DM than the treatments where the irrigation water had been restricted. Mean annual DM digestibility concentration was 66% of DM and was not affected by treatment. Similarly, mean crude protein concentration, which was 22% of DM, was also not affected by treatment. There was no consistent effect of restricted irrigation on the neutral detergent fibre concentration of the lucerne plants. These results suggest that in seasons where irrigation is restricted because of limited water supply, the reduction in lucerne productivity is not associated with a penalty in forage nutritive characteristics, with lucerne able to provide sufficient nutrients to form a large proportion of the total diet for a high-producing dairy cow.