Changes in nutrient leaching and groundwater quality during long-term studies of an arable field on the Swedish south-west coast

The aim of this study was to evaluate the long-term (1977–2004) effects of new agricultural practices and reduced acid rain on drainwater and groundwater chemistry for an intensely cultivated arable field with sandy soil in south-west Sweden. Trends in chemical composition of the drainwater were compared with those of atmospheric deposition and groundwater. A modified crop rotation including catch crops significantly decreased the average concentration of nitrate nitrogen (NO₃-N) in drainwater from 13.0 to 7.2 mg L^−l. This rotation was also found to be a very effective measure against high NO₃-N concentrations in shallow groundwater (1.7 m below the soil surface). The degree of phosphorus saturation (DPS) in the subsoil, calculated to be 10% and 9% by two different laboratory methods, corresponded to an average and constant concentration of dissolved reactive phosphate (DRP) in drainwater of 0.006 mg l^−l. Generally lower inputs of acid deposition to the soil were confirmed by a decreasing SO₄-S trend (by 3% over 24 years) in drainwater. Changes in cropping had reduced the acid load to the soil, while drainwater alkalinity showed a slow but significant positive trend amounting to 0.4% over 24 years.