Impact of Nitrogen and Organic Manures on Yield, Botanical Composition and Herbage Quality of Two Contrasting Grassland Field Margins

Grassland field margin strips, including hedge bottoms, may support a high diversity of wild flower and grass species. This diversity is threatened by applications of fertilizer nitrogen. Organic fertilizer, in the form of farm-yard manure and rain-diluted liquid slurry which only slowly release nitrogen for plant uptake, might prove less damaging. A 5-year experiment on two contrasting sheep grazed, species-rich grassland field margin sites adjoining a mature hedgerow in mid-Wales compared three levels of fertilizer N (0, 100 and 300 kg N ha−1 year−1) with farm yard manure (FYM) and rain-diluted slurry containing an average annual equivalent of 30–42 kg N ha−1 and 27–72 kg N ha−1 respectively. The aim was to assess the impact of treatments on the plant communities of the hedge bottom and field margin strip ecosystems, and to establish whether the species diversity contained within the strips could be encouraged without significantly undermining the quantity and quality of the herbage. By the end of the experiment, the forb component of both ecosystems had been drastically reduced by the high N treatment, to less than half of their original level. The organic treatments on the other hand, particularly FYM showed signs of developing species-rich communities, while at the same time providing a relatively high yielding and nutrient-rich field margin sward of high mineral content. The implications of FYM deposition, particularly in terms of nature conservation considerations are highlighted.