Changes in soil chemistry in an afforestation experiment with five tree species

Abandoned agricultural land may be used for tree plantations. This study aimed at quantifying the effects on soil chemistry almost one decade after planting. The results can contribute to the understanding of plant-soil interactions at afforestation. An experiment including birch, hybrid aspen, larch, poplar and spruce was established at four former arable sites in Sweden. Soil samples were collected repeatedly. Common for all species were decreases in soil organic carbon (SOC) pools by 13–20 Mg ha−1 or 12–18% that may be associated with former land-use and initial SOC storage. Total N pools decreased by 1.0–1.2 Mg ha−1 or 13–15%, plant-available P and Ca pools decreased by 16–26% and 14–20%, respectively. Soil CN ratios were mostly unchanged. Increases in K and Mg in upper soil (0–10 cm) and unchanged or decreased levels in lower soil (10–30 cm) suggests a redistribution by plant uptake and recycling through litter decomposition. The total K pool (0–30 cm) increased the most under larch (59%) and differed significantly from that of poplar and spruce. The pH showed a declining trend. Litter CN ratios varied among species and sites. We concluded that these early effects on soil chemistry were mainly due to cessation of annual management measures, increased nutrient uptake and altered soil physical conditions, like humidity and temperature, in the growing tree plantations. Few effects of different species could be observed at this stage.