Effects of autumn and spring defoliation management on the dry-matter yield and herbage quality of perennial ryegrass swards throughout the year

A small-plot experiment was conducted in south-west Ireland to investigate (i) the effects of pre-closing regrowth interval and closing date on dry-matter (DM) yield and sward structural and composition characteristics, during the autumn-winter and spring opening periods, and (ii) subsequent carryover effects. The study used a randomized block design with a factorial arrangement of treatments (4 closing dates x 2 opening dates) with a split plot (two pre-closing regrowth intervals). The long pre-closing (LPC) interval began on 9 August, and the short pre-closing interval (SPC) started on 15 September. The autumn closing dates were as follows: 1 October (CD1), 15 October (CD2), 1 November (CD3) and 14 November (CD4). Plots were defoliated again on 1 February (EOD) or 1 March (LOD). On the LPC treatment, herbage yield increased from CD1 (2463kg DM ha(-1)) to CD3 (3185kg DM ha(-1)). On the SPC treatment, herbage yield was similar for CD3 and CD4, indicating a ceiling in herbage accumulation. For each 1-d delay in closing date between CD1 and CD4, the opening herbage yield was reduced by 10kg DM ha(-1). Herbage quality decreased as the closing date was delayed; DMD and CP decreased by 006 and 12g kg DM-1, respectively, between CD1 and CD4. The EOD resulted in increased leaf and decreased dead proportions over the LOD treatments. A balance between autumn CD and spring OD needs to be achieved to ensure a sufficient supply of high-quality grass in spring.