Effects of extensification of sheep grazing systems on animal production and species composition of the sward

Reduce chemical inputs in grassland management

A replicated controlled trial from 1990 to 1995 on two sown agricultural grasslands in Scotland (Marriott et al. 1996) found that ceasing fertilizer input had only small effects on the vegetation over six years, if grazing continued. On plots with a grass height of 4 cm in summer (75% of the number of ewes relative to fertilized grassland), white clover Trifolium repens increased from 10% to over 20% by 1994. White clover did not increase on plots with a grass height of 8 cm in summer (42-57% of the number of ewes relative to fertilized grassland). Perennial rye grass Lolium perenne was more sensitive to autumn grazing pressure, and decreased on unfertilized plots grazed to 4 cm in the autumn (from around 60% to 33-35% by 1994). Both white clover and perennial rye grass were sown agricultural varieties. Unsown species only increased substantially in unfertilized plots left ungrazed. There were two replicates of each treatment at each of two upland sites: Hartwood Research Station in central Scotland and Sourhope Research Station in southeast Scotland. The percentage cover of different plant species in each plot was measured in 1990, 1992 and 1994, using a point quadrat.