Use of sewage sludge in silvopastoral systems under Pinus radiata D. Don: soil, tree growth, and pasture production

Short-term production in silvopastoral systems is often limited due to inappropriate soil-fertility management. Sewage sludge fertilisation could enhance productivity of silvopastoral systems (including understory and trees). After taking into account heavy metal concentrations, the main aspects related to adequate use of sewage sludge as an organic fertiliser are doses and application timing. This study compared the effect of two doses of sewage sludge (200 and 400 kg total N ha−1) applied at different dates (December, January, February, and March) with the effect of mineral fertilisation and no fertilisation on soil chemical properties (pH, total concentration of Cu and Zn and availability of Ca, Al, P, K, Mn, Mg, Cu and Zn), tree growth, and pasture production in a silvopastoral system established in an area afforested with Pinus radiata D. Don during the first 8 years of the stand. A high dose of sewage sludge (400 kg total N ha−1) applied between January and February seems to be the best option for adequate sewage sludge management, as it increased nutrient availability and, therefore, pasture production and tree growth. Sewage sludge effects on soil fertility and heavy metal concentrations should be evaluated over the long term, as there is a clear residual effect of this fertiliser for an extended period of time, which makes it very attractive as an inexpensive fertilisation input.