Phosphorus leaching from clay soils can be counteracted by structure liming

Two field experiments with drained plots on clay soils (60 and 25 % clay) demonstrated a significant reduction in leaching of total phosphorus after application of structure lime. Aggregate stability, was significantly improved. Phosphorus leaching in particulate form was significantly reduced following structure liming at the site with a very high clay content. Sites representing low (50 mg kg-1) and high (140 mg kg-1) levels of phosphorus extractable with acid ammonium lactate in topsoil displayed differing effects on leaching of dissolved reactive phosphorus. This form of phosphorus was only significantly reduced compared with the control at one site with high topsoil phosphorus status and relatively high (17-18%) degree of phosphorus saturation in the subsoil. Laboratory experiments with simulated rain events applied to topsoil lysimeters from the same site also demonstrated a significant reduction in leaching of dissolved reactive phosphorus. These findings indicate that structure liming is an appropriate leaching mitigation measure on soils with both a high clay content and high soil phosphorus status.