The effect of autumn closing date on over winter tissue turnover in perennial ryegrass (Lolium perenne L.) swards

Autumn closing date (CD) in intensive pasture-based systems influences spring herbage availability. Little is known about the impact of earlier closing of swards in autumn on sward structure. A two-year experiment was undertaken to investigate the impact of five CD on herbage production, leaf extension rate (LER), leaf senescence rates (LSR), sward free leaf lamina (FLL) content and the production and survival of tillers over winter and into spring. The five CD ranges were October 1-15 (CD1), October 16-30 (CD2), October 31--November 14 (CD3), November 15-29 (CD4), November 30-December 14 (CD5) and sward measurements were made on four measurement dates (MD): December 11 (MD1), January 6 (MD2), January 27 (MD3) and prior to spring defoliation (MD4). Thirty perennial ryegrass tillers were measured until the first defoliation in spring (average 1 March). Herbage mass was greatest in early CD and tillers had greater LER and LSR (4.6 and 4.5 mm tiller(-1) day(-1) respectively) compared to swards with a later CD (3.2 and 2.3 mm tiller(-1) day(-1) respectively). Early CD had greater parent and daughter tiller mortality than later CD (parent tiller mortality 1.1 and 0.3 +/- 0.19 tillers; daughter tiller mortality 1.1 and 0.3 +/- 0.27 tillers respectively). Early CD also had greater LER and LSR in daughter tillers (2.6 and 1.5 mm tiller(-1) day(-1), respectively) compared to late (1.5 and 0.5 mm tiller(-1) day(-1), respectively). Earlier closing of sward increased herbage mass in spring, however, there were negative implications, such as increased LSR and tiller mortality.