Water-retention characteristics and related physical properties of soil on afforested agricultural land in Finland

Abstract

In recent decades, afforestation of agricultural land in Finland has caused a substantial change in land use. To assess the potential of such former agricultural soils for production of tree crops, information on soil properties is needed. The water-retention characteristics (WRC), bulk density (BD), organic matter (OM) concentration and particle-size distribution were studied in soil on afforested agricultural land in western Finland. Sites with an OM<40% in the 0–20 cm soil layer were sampled. Undisturbed core samples were taken from the 5–10, 15–20, 25–30 and 35–40 cm soil depths at 38 profiles on 23 sites. The results suggested that the properties of former agricultural soils differ considerably from the pristine mineral forest soils. The sites studied were characterised by high OM, fine texture, gleyic properties in the soil profile and low air-filled porosity (AFP) at field capacity (−10 kPa matric potential), resulting from the predomination of small pores. AFP was, in general, less than 20% in the topmost soil layer and decreased markedly with increasing soil depth indicating deteriorating aeration. In mineral soils (OM<15% in the 0–20 cm soil depth) with a median particle size of <0.02 mm (clayey and silty soils) AFP was significantly lower than in the coarser-textured soils. In mull soils (OM 15–40% in the 0–20 cm soil depth), texture did not affect AFP. Prediction of AFP from OM was not successful because OM controlled both the upper and lower limits of AFP to a similar degree. The results indicate that high water-table level associated with the predomination of fine pores in the soil leads to potential risk of restricted aeration and reduced forest growth.