Effect of autumn deferment of grazing on subsequent growth, botanical composition and quality of two types of irrigated pasture

Abstract

An experiment was carried out at Kyabram in 1979 to determine the effects of varying the time of pasture closure in autumn on subsequent growth and changes in botanical composition and herbage quality of two types of irrigated perennial pasture, one based on ryegrass (Lolium perenne) and white clover (Trifolium repens) and the other on paspalum (Paspalum dilatatum). There were six dates of closure, ranging from early April to mid-May. Mean daily growth rates (kg dry matter/ha) for ryegrass-white clover-dominant and paspalum dominant pastures were 22.8 and 6.2 in May, 16.7 and 8.9 in June, and 11.0 and 1.6 in July respectively. Variations in pasture growth throughout the late autumn-winter period were associated with date of closure and pasture type. For each additional day by which date of closure was deferred, daily growth of the sward was reduced by 0.7 kg dry matter/ha in May, while it was increased by 0.2 kg dry matter/ha in July. Herbage digestibility was lowest in May and increased throughout the experiment. For each day by which date of closure was deferred, digestibility of the herbage on offer was reduced by 0.51, 0.16 and 0.07 units in May, June and July respectively. In addition, the digestibility of the paspalum pasture was 0.7, 1.8, 2.1 and 1.4 percentage units lower than that of the ryegrass white clover pasture in May, June, July and August respectively; however, this difference was significant only in July. The difference in productivity between the two types of pasture suggested that an advantage could be gained by renovating paspalum dominant pastures rather than saving such pastures from autumn for the dairy herd in spring.