Mixed grazing and climatic determinants of white clover (Trifolium repens L.) content in a permanent pasture

The effects of grazing regime (cattle, sheep and mixed cattle + sheep) on w hite clover content (clover dry matter as a percentage of total dry matter) were measured in a permanent pasture over a 7 year period in the west of I reland (53 degrees 17'N 8 degrees 47'E). Rotational grazing was simulated b y grazing for short intense periods of 3-4 d at 3 to 5 week intervals. In g eneral. cattle grazing resulted in higher clover content (13.5 %) compared with mixed (9.5 %) or sheep (4.9 %) grazing. The ranking of clover contents (cattle > mixed > sheep) which developed rapidly in 1990 persisted until 1 996. Clover contents under mixed grazing tracked those under cattle grazing during the first 4 years, and sheep grazing during the final 3 years. With in-year relativities in clover content among grazing regimes that existed a t the start of the grazing season persisted throughout the year. There was an indication that differences in clover content between grazing regimes at the end of grazing persisted until the following spring. A regression anal ysis of clover content in each grazing period showed strong effects of graz ing regime, generally positive relationships with mean air temperature in t he period and clover content in the preceding period, and an interaction be tween air temperature and clover content in the previous period. Implicatio ns for pasture management and experimentation are discussed. (C) 2001 Annal s of Botany Company.