ORGANIC N FERTILIZATION EFFECTS ON PASTURE ESTABLISHMENT AND FOREST FIRE PREVENTION

Soil fertility is key to ensure high pasture production. Lime and fertilizers usually improves soil chemical properties in acid soils, enhancing herbaceous pasture establishment instead of woody understory vegetation in silvopastoral systems, once established harvest that promotes fire risk and causes people death in South Europe. Once established, grazing or harvesting maintains the dominance of the herbaceous component in the silvopastoral system (Mosquera-Losada et al. 2006). Liming and fertilization also helps to maintain botanical composition of sown grasslands, leading to a better animal grazing and production and, in Galicia, to a clear reduction of forest fire risk. Increasing fertility is usually based on mineral fertilizers that are currently costly for both farmers and the environment due to fertilizer production and transport. Thus, using organic fertilizers easily available and close to the farm should be promoted. Municipal sewage sludge (SS) is a good option to increase pasture production and enhance soil pH of acid soils in Galicia (Mosquera-Losada et al., 2010), but could cause some harmful to the environment due to higher proportion of heavy metals SS has compared with soil, which needs to be evaluated at long term. This study aims at evaluating the effect of three doses of SS (160, 320 and 480 kg total N ha-1) combined or not with lime, on the botanic pasture composition, compared with control treatments (no fertilisation (NF) and mineral fertilisation (MIN)) during twelve years in a silvopastoral system established under Pinus radiata D. Don in Galicia