Extensification of grassland use in the Welsh uplands: sheep performance in years 1-6

An experiment was established in 1991 on a 25-year-old perennial ryegrass/b ent (Lolium perenne L./Agrostis capillaris L.)-dominated pasture in Wales t o study the effects of reducing nutrient inputs to previously fertilized up land pasture. The effects of the removal of applications of (1) N (denoted by CaPK) (2) N, P and K (Ca) and (3) N, P, K, and Ca (Nil) were compared wi th a treatment which received applications of all four nutrients (CaPKN) ov er a 6-year period (1991-96) in a randomized block design replicated three times. The experiment was managed under a continuous variable stocking regi me (ewes and lambs until weaning and ewes thereafter) maintaining a sward s urface height of 4.0 cm throughout the grazing season. Although individual liveweight gain of the lambs was unaffected by the treatments, there was a significant reduction (P < 0.05) in total lamb liveweight gain, ewe stockin g rate and length of grazing season as a result of the withdrawal of nutrie nts. Over the 6 years total lamb liverweight gain was reduced by 17%, 32% a nd 45% and ewe stocking rate by 21%, 36% and 49% on treatments CaPK, Ca and Nil, respectively, compared with treatment CaPKN. The effect of withdrawin g nutrient inputs on ewe stocking rate was progressive and by 1996 the Nil input treatment displayed a 63% reduction compared with the CaPKN treatment and this was also coupled with a 21-day reduction in length of the grazing season. During the post-weaning period. ewes from the Nil input treatment recorded a liveweight loss in 1995 and only a modest liveweight gain in 199 6. This coupled with significantly lower body condition scores (P < 0.01) o f these ewes in the autumn indicated that the Nil input treatment could lea d to reductions in reproductive performance.