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

Abstract

The aim of this work was to determine if autumn/winter defoliation affected the time of lucerne (Medicago sativa L.) stem extension in spring. Two experiments were established at the Field Research Centre, Lincoln University. Experiment 1 was established on 1 June 2022 using an existing two year old stand of “Force 4” lucerne. There were four canopy defoliation dates (1 June, 3 July, 17 July and 1 August). Experiment 2 repeated the treatments on the same paddock in the following year on eight defoliation dates (1 May, 15 May, 1 June, 15 June, 3 July, 17 July, 1 August and 15 August). 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 both 2022 (P = 0.20) and 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 September. 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 production.