Lucerne reduces soil moisture and increases livestock production in an area of high groundwater recharge potential

Abstract

A grazing experiment was conducted on an area with high groundwater recharge potential in northeastern Victoria from 1988 to 1992. Merino wether weaners were grazed on either lucerne (Medicago sativa) or a pasture consisting of annual species (Trifolium spp., Lolium rigidum, Vulpia bromoides, Hordeum leporinum) at 5.0, 8.75, or 12.5 wethers/ha. Lucerne pastures were rotationally grazed and annual pastures were set-stocked. Measurements included herbage mass, lucerne plant density, sheep liveweight, wool production and fibre diameter, and soil moisture potential. Herbage mass in both pasture treatments decreased with increasing stocking rate, but at 12.5 wethers/ha, lucerne herbage mass was significantly (P<0.001) greater than annual pasture herbage mass. Sheep liveweight showed similar trends. On annual pastures, wool production per sheep decreased with increasing stocking rate, whereas on lucerne, it was maintained as stocking rate increased from 8.75 to 12.5 wethers/ha. Mean wool production per ha on lucerne pasture was 14.5, 23.5, and 32.1 kg for 5.0, 8.75, and 12.5 wethers/ha, respectively, and on annual pasture it was 13.8, 21.7, and 24.8 kg. Supplementary feeding was needed on annual pastures every year at the high stocking rate. On lucerne pastures, it was unnecessary except for 3 weeks in 1991. Soil moisture under lucerne was less than under annual pasture, indicating that lucerne used more water than the annual pasture and created a larger soil water deficit, thus leading to potentially less groundwater recharge. In this environment, lucerne could be productively stocked at 12.5 wethers/ha, whereas annual pastures were less productive and could only be stocked at 8.75 wethers/ha. Furthermore, lucerne was more effective at using soil water and reducing the potential for groundwater recharge.