Effect of date of sewage sludge application on tree growth and pasture production in a Pinus radiata D. Don silvopastoral system Mosquera-Losada M.R. 1* , Freitas A.P. 1;2 , Ferreiro-Domínguez N. 1 , Rigueiro-Rodríguez A. 1 (1) Crop Production Departament. Escuela Politécnica superior. Universidad de Santiago de Compostela, 27002-Lugo, Spain. (2) Faculdade de Ciências Agrárias e Veterinárias. Unesp, 14884-900 -Jaboticabal, Brasil * Corresponding author: mrosa.mosquera.losada@usc.es Abstract Several studies have demonstrated that using sewage sludge as a fertilizer in silvopastoral systems increases both the production of pastures and the growth of trees. However, it is important to determine the appropriate period for sludge application. If sewage sludge is applied too early, nutrients can be leached and if it is too late, early use of nutrients is reduced and therefore growing season shortened. The objective of this study was to evaluate the effect of sewage sludge (100 kg N ha-1) at different dates (December, January, February and March) compared with the control treatments (with and without mineral fertilizer) on the growth of Pinus radiata D. Don trees and pasture production in Galicia (Spain). It was observed that if sewage sludge is applied on February this caused an increase pasture and tree growth, compared with those treatments fertilized in December. Introduction The integration of components livestock, agriculture and forestry is important for promoting sustainable development, animal welfare and increasing pasture production periods. Understanding how the tree component could contribute to existing production systems enables the development of technical work for the introduction and / or improvement of forestry practices and / or agroforestry on farms. The trend in recent years of the distribution of land use in Galicia, northwest of Spain, indicates a continued growth of land devoted to forest use, demonstrating also that the area required for grazing suffers a slight increase [1] which, although not sufficient to sustain the increasing number of livestock in the region. Fertilization practices are tools needed to compensate extractions made by the trees and pasture in silvopastoral systems while increasing the pasture production and quality. The evaluation of the effect of improving soil fertility on pasture production and tree growth is more important when trees are established, due to the high sensibility of trees in this time to pasture development. The use of adequate doses of sewage sludge as fertilizer supplies the needed nutrients to the soil, thus ensuring increased productivity of pasture while alleviating the problem of deposit of waste through reuse and recycling of nutrients. Proper management of sludge as fertilizer should be based on optimizing its use (dose and time of application), by balancing the needs of the pasture and trees, besides increasing nutrients to the soil, so that does not produce damage to the environment [2] [3]. The objective of this study was to study the effect of the sewage sludge application date at a dose of 100 kg N ha-1 on the soil, tree growth and pasture production in a silvopastoral system. Material and Methods The experiment was established in the Spring 2001, in Lugo (NW Spain 43º14’N, 7º 21’ W, 450 metres above sea level). This area is within the Atlantic biogeographic region and it is characterised by an average annual rainfall of 1086 mm and an average annual temperature of 11.5 ºC. The soil in the area of the experiment was an abandoned agricultural soil with a sandy texture, an acid initial water pH of 5.2 and a high percentage of organic matter (8%). In 2001, the experimental area was divided into 30 plots of 150 m2 delimited by plantation lines, in which 25 one year old trees (5x5) of Pinus radiata D. Don were planted in March of 2001, at a density of 1,667 trees per hectare (frame of 3 x 2 m). Later, in October 2001 the area was hand with 12.5 kg ha-1 Lolium perenne variety Brigantia, 12.5 kg ha-1 Dactylis glomerata variety Ártabro and 4 kg ha-1 of Trifolium repens cv Huia.