Aspects of grazing management to improve productivity and persistence of white clover in Irish grassland

White clover houses symbiotic Rhizobia bacteria that make atmospheric nitrogen (N) available for plant growth. This can reduce agriculture dependency on synthetic fertilizer N and thereby reduce financial and environmental costs of agricultural production. This study investigated certain aspects of grazing management of grassclover swards on sward clover content, herbage production and animal performance on a wet clay-loam soil at Solohead Research Farm, Tipperary, Ireland. Defoliation height (DH), defoliation interval (INT) and final winter defoliation date (FIN) were investigated under simulated grazing in summer and autumn. Treading damage was investigated within three dairy grazing systems that differed in fertilizer-N input, stocking rate and grazing season. The effects of post-grazing height (PGH) on sward clover content, herbage production and milk yield per cow was investigated in grazing systems over three entire grazing seasons. Lowering DH under simulated grazing increased sward clover content and herbage production. Under actual grazing conditions, lowering PGH did not increase sward clover content but did increase herbage production. Unlike most previous experiments, lowering PGH was not associated with any reduction in milk yield per cow. The main reasons for this were that (i) the current experiment was on grass-clover, rather than grass-only swards and (ii) treatments in the current experiment were imposed from turnout in spring to housing in winter, rather than for briefer periods in late spring/summer imposed after the grazing season had begun. Therefore, low (4 to 5 cm) DH and PGH are recommended to increase clover content and/or herbage production in 3 grass-clover swards. However, to avoid losses of milk production, target PGH should be practiced from first turnout in spring and should not be abruptly lowered during the grazing season with unsupplemented animals. Simulated grazing intervals of 21 days in summer and 42 days in autumn gave the best results in terms of balancing herbage production, herbage quality (CP and OMD) and sward clover content into the following year. These are similar to current recommendations for grass-only swards in Ireland and white clover may actually assist these aspects of grazing management by maintaining herbage nutritive value for longer periods of regrowth than grass-only swards. Extending FIN from 23 September to 16 December in the mown plots had no effect on sward clover content or clover herbage production. However, in the grazing systems, a later grazing season (April to January instead of February to November) was associated with higher sward clover contents and herbage production in the following year. The difference between the results of the two experiments may have been due to the higher grass competition generally found in grazed swards. Treading damage was associated with reductions in herbage production of both grass and clover. The effect of treading damage was greatest in spring, with reductions of herbage production by up to 58%. Particular care should be taken at this time of year, when silage ground has been removed and stocking rates are higher. More research is needed to find practical solutions that enable farmers to reduce treading damage of pasture (both grass and grass-clover) on Irish farms.