Sewage sludge fertilisation of a silvopastoral system with pines in northwestern Spain

The use of municipal sewage sludge as a fertiliser could be a more adequate means of disposal of this residue than its transport to the dump. The obje ctive of this experiment was to evaluate the effects of different doses of sludge and sowing a mixture of cocksfoot (Dactylis glomerata) and clover (T rifolium repens) on pasture production, botanical composition of the pastur e, forage quality, and changes in soil chemical properties. Treatments appl ied were: (1) no fertilisation (L0), (2) fertilisation with 26 Mg ha(-1) of sewage sludge with no sowing (L40), (3) fertilisation with 26 Mg ha(-)1 of sewage sludge and sowing with 25 kg of Dactylis glomerata L. cv Artabro (D g) and 3 kg Trifolium repens cv Huia per hectare and (4) 52 Mg ha(-1) of se wage sludge with no herbage sowing (L80). Plots were established in a silvo pastoral system with Pinus radiata D. Don at a density of 1666 trees ha(-1) (3 x 2 m). The improvement of soil fertility due to organic fertiliser app lication and the use of Dactylis glomerata increased the production and qua lity of pasture as well as reduced the risk of fire and erosion, as grasses dominated shrubs. Fertilisation with sewage sludge in soils of acid origin increased the concentration of copper in the pasture and, if cocksfoot was not sown, the levels of this element exceeded the maximum tolerable dietar y levels for sheep. On the other hand, fertilisation also increased the lev els of zinc in pasture, but values were not above toxic limits for sheep, h orses and cattle.