Pasture biodiversity after five years of establishment of a walnut silvopastoral system fertilized with different types of sewage sludge

Silvopasture is the combination of woody vegetation with forage and animal production on the same land that allows the diversification of agricultural income and productivity. In the silvopastoral systems, the fertilisation with sewage sludge could increase tree growth and pasture production at the same time that the pasture biodiversity is modified. The objective of this study was to evaluate pasture biodiversity of a walnut silvopastoral system grazed by sheep and fertilized with three types of sewage sludge (anaerobic, composted and pelletized) and with mineral fertilisation after five years of establishment. At the beginning of the experiment all plots were sown with Dactylis glomerata L., Lolium perenne L. and Trifolium repens L. Nevertheless, their presence diminished over the years probably due to the shade generated by the trees, the competence with native and less demanding species and cattle trampling. Moreover, the nitrogenous fertilisation benefited the native species such as Agrostis capillaris L., Bromus hordeaceus L. and Holcus lanatus L., which are less productive and of lower quality but more frugal and nitrophile shade-tolerant species with a higher soil seed bank compared with the sown species.