The impact of organic and inorganic fertilizers and lime on the species-richness and plant functional characteristics of hay meadow communities

Vegetation responses to fertilizers and lime applied in a seven-year study at paired unimproved and semi-improved mesotrophic hay meadows in Cumbria and Monmouthshire, UK, are described in terms of species-richness and several other plant community variables. Treatments were farmyard manure (FYM) applied at rates of between 6 and 24 tonne ha−1 annually or every third year, inorganic fertilizers giving equivalent amounts of N, P and K, and lime applied either alone or with FYM applied annually or three-yearly. Annual FYM at 24 tonne ha−1 reduced species-richness and the richness of positive indicator species at all sites and increased the proportional cover of nutrient-demanding species, whilst liming in conjunction with 12 tonne ha−1 annual FYM application was equally detrimental at the unimproved site in Wales but not in Cumbria. Inorganic fertilizers were apparently no more detrimental to vegetation quality than equivalent FYM treatments, although medium-term nutrient supply from FYM may have been underestimated. Species-richness was maintained by FYM at ⩽12 tonne ha−1 year−1 in the semi-natural northern meadow, where such levels had been used in the past, but only by amounts equivalent to ⩽6 tonne ha−1 year−1 at the Welsh sites which had no recent history of fertilizer use. It is unclear to what extent such differences are attributable to innate differences in plant community type, rather than to site-specific differences in past management. The implications of our findings for defining sustainable fertilizer practices to maintain or enhance the nature conservation value of mesotrophic meadows are discussed.