The effects of simulated summer-to-winter grazing management on herbage production in a grass-clover sward

The effects of summer-to-winter simulated grazing management factors, namely defoliation interval (INT: 21, 42, 56 or 84 d), defoliation height (DH: 2·7, 3·6, 5·3 or 6·0 cm) and final defoliation date (FIN: 23 September, 4 November or 16 December) on herbage production in a grass-clover sward were studied. Treatments were imposed between July and December 2008, with all plots under common management in the following March to June 2009. The 42-d INT achieved the highest (P < 0·001) total herbage yield at 11·00 t DM ha^-1. Shorter (21 d) and longer (56-84 d) intervals reduced annual clover herbage yield and biological nitrogen fixation estimates. Lowering DH from 6·0 to 2·7 cm in the summer-to-winter period increased sward clover content and clover herbage yield through to the following June, 6 months after treatments ended. Delaying FIN from 23 September to 16 December had no significant effect on annual clover, grass or total herbage yield. Spring-summer clover herbage yield was positively correlated with spring-summer clover stolon mass (R² = 0·54, P < 0·001) and, to a lesser extent, light penetration through the sward in the previous winter (R² = 0·16, P < 0·05). A 42-d INT with low DH (2·7-3·5 cm) is therefore recommended for grass-clover swards.