The effects of fertilization with anaerobic, composted and pelletized sewage sludge on soil, tree growth, pasture production and biodiversity in a silvopastoral system under ash (Fraxinus excelsior L.)

摘要

In silvopastoral systems, tree growth and the composition and productivity of pasture can be modified by management practices such as initial fertilization when tree seedlings are more sensitive to understorey competition. The aim of this study was to compare the effects of fertilization with different types of sewage sludge (anaerobic sludge, composted sludge and pelletized sludge), using different rates of incorporation and mineralization with traditional treatments (with and without mineral fertilizers) on the growth of newly established ash (Fraxinus excelsior L.) and on pasture development, to obtain sustainable management practices that enhance the growth of both components. Soil characteristics, tree growth, sward composition and pasture development were modified differently according to the type of sewage sludge used, and for similar total nitrogen inputs. Anaerobic sludge had a higher initial effect on both tree and pasture productivity. Pelletized sludge sustained better tree and pasture production. Composted sludge was found to be the most appropriate treatment for improving soil characteristics over the long term on sandy soils. It was concluded that pelletized sludge should be promoted because it enhances productivity, allows for better nutrient recovery and is less costly to store and apply compared with anaerobic sludge and composted sludge. No toxic concentrations of Zn or Cu were found in plants or in the soil despite higher concentrations being present in the applied sludge than in soil.