Despite the extensive literature on the effect on soil properties of afforestation of former arable land, we still lack full understanding of whether the changes proceed in the same direction and at the same rate, and of how long is required to achieve a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a study comparing post-arable sandy soils (Dystric Arenosols) afforested with Scots pine (Pinus silvestris L.) with arable soils and soils of continuous coniferous forests, the range and direction of changes in pH, organic carbon (C org ), total nitrogen (N tot ), ammonium (N-NH 4 ) and nitrates (N-NO 3 ) in soil solution, total (P tot ) and available (P av ) phosphorus were determined. The studies were carried out in south-east Poland (51°30′-51°37′N, 22°20′-22°35′E). Ten paired sites of afforested soils (five with 14-to 17-year-old stands and five with 32-to 36-year-old stands) with adjacent cultivated fields, and five sites of continuous forest with present stands of ca. 130-150 years old were selected. Soil samples were taken from the whole thickness of master horizons and, in the case of the A horizon of the afforested soils, from three layers: 0-5 (A 0-5 ), 5-10 (A 5-10 ) and 10-20 cm (A 10-20 ). The cultivated soils in the Ap horizon showed higher pH (by ca. 1.0 unit), lower C org and C:N, similar N tot , lower N-NH 4 , higher N-NO 3 , higher P tot and P av contents compared with the Ah horizon of continuous forest soils. The results indicated decreased soil pH in the former plough layer of the afforested soils, with the greatest decrease observed in the 0-5 cm layer. In these soils, the C org content was considerably higher in the A 0-5 layer, but lower in the two deeper layers and in the whole A horizon (0-20 cm) compared with the Ap horizon of the arable soils. The results indicate that the C org content, after an initial phase of decline, again achieved a level characteristic of arable soils. The N tot content in all layers of the A horizon of the afforested soils was lower than in the Ap horizon of the arable soils, and showed a reduction with stand age, especially in deeper layers. The C:N ratios in the mineral topsoil increased with stand age. N-NH 4 content increased and N-NO 3 decreased after afforestation. The P tot and P av contents in all layers and in the whole A horizon of the afforested soils, on stands of both ages, was lower than in the Ap of the cultivated soils. From the results, it could be concluded that, after more than 30 years of tree growth, the soils of the A horizon were still more similar to arable than to continuous forest soils with respect to C org , P tot and P av . With respect to pH, N-NH 4 and N-NO 3 , especially in the 0-5 cm layer, they were more similar to continuous forest soils than to Plant Soil (2008) 305:171-187

Despite the extensive literature on the effect of afforestation of former arable land on soil properties, we still do not fully understand whether the changes proceed in the same direction and at the same rate or how long it takes to achieve a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a comparative study of post-arable sandy soils (Distric Arenosols) afforested with Scots pine (Pinus silvestris L.) with respect to arable soils and soils of continuous coniferous forests, a range and direction of the changes in some of their physical and sorptive properties were determined. The studies were carried out in SE Poland, 51°30′-51°37′N, 22°20′-22°35′E. Ten paired sites of the afforested soils (five with 14-to 17-year-old stands and five with 32-to 36-year-old stands) with adjacent cultivated fields and five sites of continuous forests with present stands of ca. 150 years were selected. For the physical properties, undisturbed soil cores were sampled from the upper part of each horizon while in the case of A horizon of the afforested soils, from two layers: 0-5 cm and 10-15 cm. For the remaining analyses, soil was taken from the whole thickness of the master horizons and in the case of A horizon of the afforested soils, from three layers: 0-5, 5-10 and 10-20 cm. The following properties were analysed: texture, bulk density (BD), total porosity (TP), water content at potential of −0.098, −9.81 and −49.03 kPa, hydrolytic acidity (Ha), base exchangeable cations: Ca 2+ , Mg 2+ , K + , Na + , total exchangeable bases (TEB), cation exchange capacity (CEC) and base saturation (BS). Afforestation caused a decrease in BD, an increase in TP and had no affect on water properties when compared with the cultivated soils. The changes referred to the A horizon, particularly to its 0-5 cm layer, and were related to the stand age. The CEC gradually rose in the former plough layer, beginning from the uppermost part, but during the first two decades its increase in the 0-5 cm layer was offset by a decline in the deeper layers. No substantial increase in CEC, in the whole A horizon, was recorded until three to four decades of afforestation. Afforestation also invoked an increase in Ha, a drop in TEB, particularly Ca 2+ , Mg 2+ and K + , and reduction in BS. No differences between soils for all the studied properties for B and C horizons were observed. It was noted that more than 30 years after afforestation, the TEB and BS as well as Ca 2+ , Mg 2+ and K + content differed substantially, but in most cases not significantly, from their values in the cultivated soils and reached a level more similar to the soils of continuous coniferous forests. With respect to the water properties, Ha and CEC of the afforested soils still resembled arable soils, whereas regarding the TP and BD, they were somewhere in the middle. This implies that to Plant Soil (2008) 305:157-169 understand changes in the soil properties resulting from afforestation and to predict future trends, long-term research is needed.