Residual effects of lime and sewage sludge inputs on soil fertility and tree and pasture production in a Pinus radiata D. Don silvopastoral system established in a very acidic soil

In Galician (Spain) silvopastoral systems, nutrient availability to the pasture and trees can be limited by soil acidity. Liming and fertilisation with sewage sludge could enhance the productivity of silvopastoral systems (including understory and trees) by increasing Ca and reducing Al in the soil. This study evaluated changes in soil chemical properties, tree growth and understory production in test plots, both limed and unlimed, in a silvopastoral system located on an acidic forest soil under Pinus radiata D. Don. This research compared the effects of different doses of sewage sludge (160, 320 and 480 kg total N ha−1) with the effects of mineral fertilisation (8% N – 24% P2O5 – 16% K2O) and no fertilisation. The initial lime applications improved soil fertility (increasing soil pH, effective exchange capacity, and the saturation percentage of Ca and reducing the saturation percentage of Al) more than the sewage sludge. However, the most significant effects of sewage sludge were found over the long term after high doses of sewage sludge were applied (480 kg total N ha−1). Therefore, the use of sewage sludge as a fertiliser improves both soil fertility and the productivity of silvopastoral systems in the long term as long as an adequate disposal of this residue is guaranteed.

► Lime has an earlier positive effect than sewage sludge on soil fertility.
► The positive effects of sewage sludge on soil fertility last for more than six years.
► Mineral fertilisation significantly diminished soil fertility (ECC and soil pH).
► High dose of sludge and lime almost doubled production compared with control.