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 × 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 ( CD 1), 15 October ( CD 2), 1 November ( CD 3) and 14 November ( CD 4). Plots were defoliated again on 1 February ( EOD ) or 1 March ( LOD ). On the LPC treatment, herbage yield increased from CD 1 (2463 kg DM ha −1 ) to CD 3 (3185 kg DM ha −1 ). On the SPC treatment, herbage yield was similar for CD 3 and CD 4, indicating a ceiling in herbage accumulation. For each 1‐d delay in closing date between CD 1 and CD 4, the opening herbage yield was reduced by 10 kg DM ha −1 . Herbage quality decreased as the closing date was delayed; DMD and CP decreased by 0·06 and 12 g kg DM −1 , respectively, between CD 1 and CD 4. 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.