Effects of the timing and intensity of spring grazings on reproductive development, tillering, and herbage production of perennial ryegrass dominant pasture

Abstract

Reproductive development, tillering, and herbage production were studied in mixed pastures containing ‘Grasslands Nui’ perennial ryegrass (Lolium perenne L.) and ‘Grasslands Huia’ white clover (Trifolium repens L.), which were rotationally grazed by sheep. The effects of interruption of ryegrass reproductive development during early culm elongation (TI) or 30% inflorescence emergence (T2), by either hard grazings (H; residual leaf area index (LAI) 0–0.7) or lax grazings (L; residual LAI 0.8–2.2) were compared. These grazing intensity treatments were continued until mid summer; and in late summer and autumn all pastures received the same grazing management. Culm elongation in an initial group of reproductive tillers, 2400/m², started in October, and 30% inflorescence emergence occurred in mid November. During November and December a further 1000/m² secondary reproductive tillers appeared. Few new reproductive tillers appeared after December. Vegetative ryegrass tiller density declined markedly during reproductive growth, but the differences between T1 and T2 at 30% inflorescence emergence had disappeared a month later because of rapid tillering. Ryegrass tiller density was greater in H than L from mid summer until the end of the experiment in winter, mainly because of a difference in tillering during summer. In winter, a higher density of Poa tillers was recorded in L than H. The grazing treatments did not significantly affect herbage accumulation. This averaged 12.7 t DM/ha over 38 weeks of measurement. However, a higher proportion of lamina, and a lower proportion of stem, accumulated in T1 than T2. A higher proportion of green herbage, and a lower proportion of dead herbage, accumulated in H than L.