MANAGEMENT OF LOLIUM-PERENNE TRIFOLIUM-REPENS PASTURES IN THE SUBTROPICS .2. EFFECT OF SUMMER DEFOLIATION, IRRIGATION DURATION, SEEDBED PREPARATION AND PASTURE TYPE

This study on the north coast of New South Wales, Australia, evaluated the effect of irrigation and defoliation management over summer, pasture type and seedbed preparation on production and survival of a perennial ryegrass pasture over an 18-month period from sowing. In a relatively dry summer, irrigation sufficient only to keep plants growing, increased production of ryegrass plus clover from 2826 to 5515 and 3210 to 5396 kg DM/ha in summer and the subsequent autumn/winter, respectively, and increased survival of ryegrass plants by 34%. The more summer active Olwen white clover/NZA895 perennial ryegrass combination had a 16% higher production in summer, but a 11% lower production in winter than a Haifa/Yatsyn sward. The difference in production was entirely due to the clover component of the pasture. DM yield in the first growing season for the ryegrass/white clover pasture was equivalent to applying 20 kg N/ha/month to a pure ryegrass sward. In the subsequent summer/autumn/winter, the yield of pure ryegrass pasture was well below the ryegrass/white clover swards at any rate of N application. There was no difference between survival of NZA895 and Yatsyn ryegrass or incursion of summer grass into their respective plots. Plots defoliated over summer at 6 cm, as opposed to 12 cm, stubble height yielded 54% more edible DM and resulted in a 65% higher ryegrass plant survival rate. There was no effect on summer grass incursion. Multiple cultivations appear to be the key to appropriate seedbed preparation, with this treatment achieving the highest ryegrass survival rate, lowest summer grass incursion and highest DM yields.