Effect of closing date and harvest date on yield and quality of a perennial ryegrass-white clover sward in spring

Abstract

Ninety-six plots (each 3 by 2 m) of perennial ryegrass-white clover pasture were randomly allocated within 4 replicate blocks to each of 3 closing date x 8 harvest date treatments to determine the effect of closing date on yield and quality of herbage produced over spring. Closing dates were 19 August (CLD 1), 9 September (CLD 2) and 30 September (CLD 3). Harvest dates were at weekly intervals from 14 October to 2 December. The increase in dry matter (DM) with time from closing was best described by a straight line relationship with DM yield increasing by an average of 104 kg/ha.day for the earlier closing dates and a quadratic relationship for CLD 3, reaching 7026,5732 and 4287 kg DM/ha on 2 December for CLD 1,2 and 3 respectively. From an initial digestibility of 74.2, 77.1 and 78.8% on 14 October, for CLD 1, CLD 2 and CLD 3 respectively, herbage quality dropped rapidly over the harvest period by about 2.8% per week and was below 65% by 11 November for the earlier closed treatments and 1 week later for the 30 September closing. DM yield was also maximised by late harvest (late November), which allowed pasture to grow uninterrupted through the reproductive phase. Early harvest (mid October) was necessary to maximise herbage digestibility because of the rapid decline in herbage quality in spring. Therefore, optimum harvest date depended on compromising either quality or yield of pasture, which illustrates the need to consider the 'end use' of conserved fodder when selecting harvest date.