The effect of strategic nitrogen application and defoliation systems on the productivity of a perennial ryegrass/white clover sward

The productivity of a mixed sward comprising perennial ryegrass cv. Fantoom and white clover cv. Aran was measured under eight defoliation management systems and two fertilizer N rates (0 and 75 kg ha^‐1) applied in spring. The defoliations involved a basic six‐harvest simulated grazing system together with the interposition of silage cuts once or twice at varying times during the growing season; evaluation was made over three harvest years, 1983‐85. Mean annual production of total herbage DM over the three years was 8.351 tha^‐1 without N and 9.49 tha^‐1 with 75 kg N ha^‐1, a mean response of 15.2 kg DM per kg applied N. The responses for individual treatments occurred mainly at the first cuts, whether for simulated grazing (a mean of 12 9 kg DM) or for silage (a mean of 259 kg DM); however, this influence of spring N was not sustained at other cuts over the season. Mean annual white clover DM production was 4.19 t ha^‐1 with no N and 3.32 t ha^‐1 with 75 kg ha^‐1 N, but the reduction due to N was not significant in any year. The mean amount of clover stolon DM present post harvest over all management systems was 1.33 t ha^‐1 with no N and 1.03 t ha^‐1 with 75 kg ha^‐1 N. Mean annual DM production of total herbage from the six‐harvest system was 8.11 t ha^‐1 Compared with 8 88 t ha^‐1 (a 9% increase) from the systems with one silage cut and 9.241 ha^‐1 (a 14% increase) from the systems with two silage cuts. Corresponding white clover DM production was 4.02, 3 87 and 3 53 t ha^‐1, respectively, and mean stolon DM amounts post harvest, 1 12,1.15 and 1‐23 t ha^‐1, respectively. It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. Spring N application did not greatly reduce white clover production in this experiment where white clover was at higher levels than are likely in farming practice and the swards were not grazed. More knowledge of spring N rates, and indeed of N application rates generally, would be advantageous in future assessment of silage cutting systems.