Spring growth of lucerne (Medicago sativa L.) after different times of winter defoliation

The aim of this work was to determine if autumn/winter defoliation affected the time of lucerne stem extension in spring. Two experiments were established at the Field Research Centre, Lincoln University. Experiment 1 was established on 01/06/2022 using an existing two year old stand of “Force 4” lucerne. There were four canopy defoliation dates (1/06, 03/07, 17/07, 1/08). Experiment 2 repeated the treatments on the same paddock in the following year on eight defoliation dates (1/5, 15/5, 1/6, 15/6, 3/7, 17/7, 1/8 and 15/8). In both experiments, five stems were marked in each plot and stem height was measured weekly. The start of stem extension was unaffected by canopy defoliation date in either 2022 (P = 0.20) or 2023 (P = 0.17). Initiation of stem extension was triggered by a base photoperiod of 11.1 ± 0.2 h. This meant the thermal time accumulated from final defoliation to the start of stem extension differed among treatments. These results suggest the time of autumn/winter defoliation (the winter clean-up graze) will not affect the time of the first spring grazing, provided the developing basal buds are not removed. All stands reached 150 mm height by mid-September and produced 3.0 t/ha of dry matter by the end of the month. This suggests, grazing of the first paddock at Lincoln should commence in the first week of September to create a staggered start to rotational grazing that can maximise lucerne yield and quality for animal liveweight production.