Response to sewage sludge fertilisation in a Quercus rubra L. silvopastoral system: Soil, plant biodiversity and tree and pasture production

Silvopastoral systems are sustainable form of land management promoted by European Union. The productivity of the herbaceous and tree components in a silvopastoral system could be limited by soil fertility. The use of adequate doses of organic fertilisers like sewage sludge could enhance the productivity of both pasture and trees and promote biodiversity. The quantification of the best dose of sewage sludge to be applied in a silvopastoral system is important in order to enhance production and biodiversity in a silvopastoral system, while avoiding nitrate contamination of the ground water. This study aims to evaluate the effects of different doses of sewage sludge (100 kg total N ha−1, 200 kg total N ha−1 and 400 kg total N ha−1) on different variables of soil (soil pH, effective exchange capacity and the saturation percentage of Al, K, Ca, Mg and Na), tree growth and pasture (production, species richness and botanical composition) as compared to the fertilisation treatment in a silvopastoral system under Quercus rubra L. Sewage sludge applications initially improved soil nutrient levels (effective exchange capacity and Ca saturation percentage) and subsequently pasture production and tree growth when 200 and 400 kg of total N ha−1 were applied. On the other hand, the establishment of pasture and trees improved soil conditions at a medium term due to the organic matter input into the sandy soil, which increased species diversity specially at a 100 kg of total N ha−1 dose.

Research highlights
► Sewage sludge improves soil characteristics at a short term.
► The use of the sludge as fertilizer increases productivity at medium term in Quercus rubra afforested lands.
► Pasture and tree establishment in a sandy soil improves soil characteristics at medium term.
► Biodiversity, mainly of dicot species, is improved as soil cation availability is increased.