Increased use of artificial fertilizers has caused widespread loss of species-rich grasslands throughout Britain and mainland Europe. Species-rich meadows are traditionally managed by hay cutting, use of farmyard manure (FYM) and occasional liming, but sustainable fertility management to maintain their botanical diversity is ill defined. This study measured vegetation responses to fertilizers and lime applied over 12 years to species-rich upland and lowland mesotrophic hay meadows in the UK. Treatments consisted of three rates of FYM applied annually or triennially, inorganic fertilizers giving equivalent amounts of N, P and K to two of the annual and two of the triennial FYM treatments, and lime applied either alone or with annual or triennial FYM. Farmyard manure at 24 tonnes ha-1 year-1 reduced total species richness and the richness of positive indicator species at both meadows and increased aggregate cover of negative indicator species. Lower rates of FYM application were also detrimental at the lowland meadow, but not at the upland one. Inorganic fertilizers were no more damaging to plant species richness than equivalent FYM treatments. At the upland meadow, vegetation quality was maintained by continuing past FYM inputs (12 t ha-1 year-1), but improved at lower rates. At the lowland meadow, which has no recent history of fertilizer use, rates equivalent to only ≤4 tonnes FYM ha-1 year-1 were sustainable. Evidence was slight of vegetation adapting to increased inputs at either meadow. Between-meadow differences in vulnerability to treatments apparently reflected differences in site-specific factors, particularly past management, rather than differences in plant community type. Synthesis and applications. Relatively modest fertility inputs can reduce the ecological value of meadows with no recent history of such inputs, whereas moderate inputs of fertilizer and lime will be ecologically sustainable in meadows adapted to a long history of application. Decisions on sustainable levels of fertilizer use to maintain or enhance botanical diversity of grassland should be based on knowledge of soil physical and chemical status and past fertility management. Inorganic fertilizers are no more damaging than farmyard manure when applied at equivalent amounts of N, P and K. © 2013 The Authors. Journal of Applied Ecology © 2013 British Ecological Society.