Mineral concentrations in herbage and soil in a Pinus radiata silvopastoral system in north-west Spain after sewage sludge and lime application

Silvopastoral systems in north-west Spain can reduce the risk of fires and promote multi-purpose forest land use. Fertilizer application is important for optimal pasture and tree production. The application rate of sewage sludge as a fertilizer is regulated and is based on its nutrient concentration, especially nitrogen. The aim of this study was to assess the effect of three consecutive years of application of different application rates of sewage sludge and inorganic fertilizer, with or without lime (2·5 t CaCO₃ ha^?1) on the ammonium, nitrate and exchangeable K, Ca and Mg contents in soil, and on the crude protein (CP), K, Ca and Mg concentrations in herbage in a silvopastoral system established under a 5-year-old Pinus radiata D. Don plantation with a density of 1667 trees ha^?1. The experiment was started in autumn 1997, when a pasture mixture was sown (25 kg ha^?1 Lolium perenne , 10 kg ha^?1 Dactylis glomerata and 4 kg ha^?1 Trifolium repens ). Changes in ammonium and nitrate content in the soil in response to liming and sewage sludge application reflected the initial pH of the soil. In general, liming increased the available Ca and Mg content in soil, and CP and Ca concentrations in herbage, but reduced exchangeable K content in the soil in the first year. Application of sewage sludge increased all of the measured nutrients in both soil and herbage.