Management of Lolium perenne/Trifolium repens pastures in the subtropics. I. Effect of defoliation interval, seeding rate and application of N and lime

Abstract

This plot cut study, conducted on the subtropical north coast of New South Wales, evaluated the effect of defoliation interval, seeding rate and application of nitrogen and lime on production and survival over summer of a Lolium perenne/Trifolium repens pasture. There was a 117% or 12 781 kg DM/ha difference in DM yield between the worst and best treatment combinations over the 17 month period of the study. The best treatment combination for yield also gave the highest rate of ryegrass survival and lowest levels of 'summer grass' ingression over the first summer. Defoliation at 4 weeks or 'when ready' (before onset of senescence, 'lodging' or rust), compared to at 2 weeks, increased DM yield by 18 and 32% in year 1 and 41 and 59% in year 2 respectively. The larger difference in year 2 was primarily due to a greater ingression of 'summer grass' (winter dormant) and a lower survival of ryegrass plants over the first summer in the most frequently cut plots. The lower root DM in summer at the more frequent cutting interval may have been one factor responsible for the defoliation effect. DM yields of a 'clover dominant' sward (nil N except at sowing and 8 kg ryegrass/ha; clover = 53%) was 85% in year 1 and 50% in year 2 (up to August) of that of a 'ryegrass dominant' sward (100 kg urea ha-1 mo-1 and 35 kg ryegrass/ha; clover = 8%). The lower yield of the 'clover dominant' pasture in year 2 was partly due to a greater level of 'summer grass' infestation. Application of N increased plant survival over summer, but under grazing, many plants may have been lost through sod pulling by stock, as roots were more restricted to the surface. Application of lime increased DM yield in both years.