Effects of lime and swage sludge on soil, pasture production, and tree growth in a six-year-old Populus canadensis Moench silvopastoral system

In many regions worldwide, silvopastoral systems are implemented to enable sustainable land use allowing short, medium, and long-term economic returns. However, the short-term production in silvopastoral systems is often limited due to nonappropriate soil-fertility management. This study evaluated the effects of two doses of lime (0 and 2.5 t CaCO3 ha–1) and three sewage-sludge treatments (0, 200, and 400 kg total N ha–1 y–1 applied in 2 consecutive years) on soil characteristics (soil pH, soil organic matter [SOM], soil nitrogen, cation-exchange capacity [CEC]), pasture production, and tree growth in a silvopastoral system of Populus × canadensis Moench in Galicia, northern Spain during 6 years after establishment. Soil pH increased during the experimental period for all treatments, although this effect was more pronounced after lime application. Changes in SOM and soil nitrogen content were not consistent over time, but sewage-sludge application seemed to result in higher values. Higher CEC was found for treatments with lime and sewage-sludge application. Following incorporation of lime and sewage sludge, pasture production was significantly enhanced (cumulative pasture production 51.9 t DM ha–1 for Lime/N400 compared to 39.0 t DM ha–1 for No lime/N0). This higher pasture production also affected tree growth due to more severe competition between pasture and tree resulting in slower tree growth. Liming and application of sewage sludge are relevant measures to improve soil fertility and thereby optimizing the overall production of silvopastoral systems. However, it is important not to overintensify pasture production to ensure adequate tree growth