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)\navailable for plant growth. This can reduce agriculture dependency on synthetic\nfertilizer N and thereby reduce financial and environmental costs of agricultural\nproduction. This study investigated certain aspects of grazing management of grassclover\nswards on sward clover content, herbage production and animal performance on\na wet clay-loam soil at Solohead Research Farm, Tipperary, Ireland.\nDefoliation height (DH), defoliation interval (INT) and final winter defoliation date\n(FIN) were investigated under simulated grazing in summer and autumn. Treading\ndamage was investigated within three dairy grazing systems that differed in fertilizer-N\ninput, stocking rate and grazing season. The effects of post-grazing height (PGH) on\nsward clover content, herbage production and milk yield per cow was investigated in\ngrazing systems over three entire grazing seasons.\nLowering DH under simulated grazing increased sward clover content and herbage\nproduction. Under actual grazing conditions, lowering PGH did not increase sward\nclover content but did increase herbage production. Unlike most previous experiments,\nlowering PGH was not associated with any reduction in milk yield per cow. The main\nreasons for this were that (i) the current experiment was on grass-clover, rather than\ngrass-only swards and (ii) treatments in the current experiment were imposed from\nturnout in spring to housing in winter, rather than for briefer periods in late\nspring/summer imposed after the grazing season had begun. Therefore, low (4 to 5 cm)\nDH and PGH are recommended to increase clover content and/or herbage production in\n3\ngrass-clover swards. However, to avoid losses of milk production, target PGH should be\npracticed from first turnout in spring and should not be abruptly lowered during the\ngrazing season with unsupplemented animals.\nSimulated grazing intervals of 21 days in summer and 42 days in autumn gave the best\nresults in terms of balancing herbage production, herbage quality (CP and OMD) and\nsward clover content into the following year. These are similar to current\nrecommendations for grass-only swards in Ireland and white clover may actually assist\nthese aspects of grazing management by maintaining herbage nutritive value for longer\nperiods of regrowth than grass-only swards.\nExtending FIN from 23 September to 16 December in the mown plots had no effect on\nsward clover content or clover herbage production. However, in the grazing systems, a\nlater grazing season (April to January instead of February to November) was associated\nwith higher sward clover contents and herbage production in the following year. The\ndifference between the results of the two experiments may have been due to the higher\ngrass competition generally found in grazed swards.\nTreading damage was associated with reductions in herbage production of both grass\nand clover. The effect of treading damage was greatest in spring, with reductions of\nherbage production by up to 58%. Particular care should be taken at this time of year,\nwhen silage ground has been removed and stocking rates are higher. More research is\nneeded to find practical solutions that enable farmers to reduce treading damage of\npasture (both grass and grass-clover) on Irish farms.