Accumulation of phosphorus in cultivated soils phosphate phase, sorption and desorption properties

本报告包括以下三点。1. Andisols的磷酸盐吸附和解吸机制的粘土级分的六个脲基甲酸盐和非脲基甲酸盐Andisols从日本东北部被用来确定与磷酸盐吸附的反应。当磷酸盐吸附在这些材料上时，溶解在低pH溶液中的铝沉淀，正电荷量减少，pH升高，硅酸盐和有机物释放，负电荷量增加。各反应的贡献取决于土壤类型、pH值和磷的吸附量，当磷从这些材料上解吸时，负电荷量减少。2.近晶土对磷的吸附机理耕作近晶土中虽然活性铝和铁的含量远低于Andisol，但含有大量的交换性Ca和Mg。这些交换性阳离子与磷酸盐反应生成CaHPO_4·2H_2O和MgNH_4PO_4。2O，pH 7.3左右。有机还原剂对磷酸化水合氧化铁中磷酸盐的释放具有螯合作用的还原剂如查特可和抗坏血酸对磷酸化水合氧化铁中磷酸盐的释放效果比不具有螯合作用的还原剂好。

This report consists of the following three points. 1. Mechanism of phosphate sorption and desorption of Andisols Clay fractions of six allophanic and nonallophanic andisols from northeastern Japan were used to determine the reactions associated with phosphate sorption. When phosphate was sorbed on these materials, aluminum dissolved in the solution at low pH precipitated, the amount positive charge decreased, pH rose, silicate and organic matter was released and the amount negative charge was increased. Contribution of the individual reactions depends on the type soils, pH and the amount of phosphate sorbed.When phosphate was desorbed from these materials, the amount of negative charge was decreased. 2. Mechanism of phosphate sorption on smectic soilsCultivated smectic soils contain large amount of exchangeable Ca and Mg though the contents of active aluminum and iron are much less than those for Andisols. These exchangeable cations react with phosphate to form CaHPO_4.2H_2O and MgNH_4PO_4._2O at around pH 7.3. Release of phosphate from phosphated hydrous iron oxide using organic reducing agentsReducing agents having chelating effect such as chatecol and ascorbic acid showed higher effect for phosphate release from phosphated hydrous iron oxide than those without chelating effect.