Long-term effects on sward composition and animal performance of reducing fertiliser inputs to upland permanent pasture

Abstract

This study investigated the long-term effects on sward composition and animal performance of applying different fertilizer regimes to upland permanent pasture. The experiment, which was carried out in 2008, was based on a set of replicated (n = 3) plots that had been established in 1990. The effects of applying (i) N, P, K and lime, (ii) P and K plus lime and (iii) lime only were compared with a treatment that received no nutrient applications. Using a put-and-take stocking system, the plots were grazed to a target sward surface height of 4 cm by ewes and lambs from April to early August and by ewes only from August to mid-October. The long-term reduction in nutrient inputs had led to decreases in the percentages of both sown and unsown grass species within the sward (P <0·05), and an increase in the percentage of mosses and litter (P <0·05), with a corresponding reduction in nutritional value. Although there were no statistically significant treatment-related differences in lamb growth rates, lower fertilizer inputs were associated with a marked decline in stock carrying capacity and associated overall productivity during both the pre- and post-weaning periods (P <0·001). The findings highlight the challenges faced when attempting to reconcile production and environmental objectives in upland systems.