Soil and pasture evolution of zinc in a silvopastoral system developed under Quercus rubra L. after fertilization with different doses of sewage sludge

One option adopted in many countries around the world is the use of sewage sludge as fertilizer in agriculture. However, the use of this residue as fertilizer must take into consideration its heavy metal concentration (mainly Zn), which is higher than that normally found in soils and may lead to crop toxicity and environmental degradation. The aim of this study was to evaluate the effects of different doses of municipal sewage sludge (100, 200 and 400 kg total N ha–1) on the total and available Zn concentrations in soil and the Zn levels of pasture compared to control treatment (no fertilization) in a silvopastoral system under Quercus rubra L., and a sown sward with Dactylis glomerata L., Lolium perenne L. and Trifolium repens L. during the four years after the study was established in Galicia (Spain). The results showed that fertilization with sewage sludge increased the concentration of Zn in the soil and plants, mainly when high doses of sewage sludge were applied (400 kg total N ha–1), but never exceeded the maximum values set by Spanish regulations and did not cause harmful effects on plants and animals.