The implications of spring grazing management on animal liveweight gain, yield and root reserves of lucerne (Medicago sativa L.)

Abstract

Lucerne (Medicago sativa L.) is an important legume for New Zealand dryland farms. To ensure the productivity and persistence of lucerne stands rotational grazing is recommended. However, over spring ewes and lambs are typically set-stocked for ease of management. Two grazing experiments were therefore imposed on lucerne stands to quantify the effect of spring grazing management treatments on the animal and plant production, particularly the persistency of the lucerne stand through the perennial reserves composition and quantity. The overall liveweight gains were similar between treatments with rotational having 894 kg LW/ha, semi set-stocked 881 kg LW/ha, and set-stocked having 890 kg LW/ha. The rotational treatments total dry matter production was 12,106 kg DM/ha. Plant population was the highest under set-stocked treatments with 206 plants/m², but it also had the biggest decline, to 134 plants/m² in May. The rotational treatments had the highest total root weights across all treatments, with 4,682 kg/ha, compared to semi set-stocked and set-stocked with 3,443 and 3,989 kg/ha, respectively. Although liveweight gains between treatments were similar, the carbon and nitrogen reserves in the rotational treatments were higher than semi set-stocked and set-stocked treatments. This implies that the persistence of the rotational stand will be greater than the semi set-stocked and set-stocked stands. However, results suggest that set-stocking for a short period of time (e.g. a month) is possible over spring provided that lucerne growth exceeds demand.