Fertilization in Agroforestry Systems (PA)

Fertilization is one of the most important practices that a farmer has to carry out in its farm. Fertilization can be carried out with organic or inorganic fertilizers. Experiments conducted in Galicia in silvopasture systems showed the different behaviour of the inorganic fertilization and the sewage sludge addition on productivity and biodiversity linked to the soil acidity. The experiments consist of applying sewage sludge in neutral (water pH close to 7) and very acidic (water pH of around 4.5) soils and compare them with the use of mineral fertilizers and no fertilization in silvopasture systems, as usually grasslands are fertilized but afforested lands in former croplands/grasslands areas are not fertilized at all. In soils with water pH close to 7, mineral fertilization caused a significant increase of pasture production that was in detriment of tree growth. The opposite happened when no fertilization was added: the fertility of the soil was high enough to increase tree growth but the lack of nitrogen reduced the potential pasture growth. When sewage sludge was added, both tree and pasture were growing similarly to the no fertilization and mineral treatment, respectively.