pH对土壤吸持磷酸根的影响及其原因

本文选择了浙江、江苏15个性质变化范围较大的土壤样品,研究在两种支持电解质、不同pH条件下对磷酸根的吸持反应。结果表明,加碱提高强酸性土壤的pH值,导致交换性铝的水解和羟基铝聚合物的生成,增加对磷的吸持。磷酸根同酸性土壤的反应,可促进交换性铝的水解,释放出H⁺,降低体系的pH。在CaCl₂介质中,当pH>6时,可能有磷酸钙类盐形成,使溶液中磷浓度显著降低。有机质对土壤吸持磷有重要影响。在低pH下有机质通过与Al³⁺形成络合物,阻碍溶液中A1³⁺的水解,并与磷酸根竞争羟基铝化合物表面的反应点位,从而降低酸性土壤对磷酸根的吸附量。

THE EFFECT OF pH ON PHOSPHATE SORPTION IN SOILS AND ITS POSSIBLE MECHANISM

Fifteen soil samples were collected from Zhejiang and Jiangsu provinces to study the mechanism of phosphate sorption by soils in relation to the kinds of canon of supporting electrolyte and the change of soil pH values through equilibrium.Increasing the pH of strong acidic soil by adding base resulted in the,hydrolysis of exchangeable Al and formation of polymeric hydroxy-Al species which increased the sorption of added P,The reaction of phosphate with acidic soil might promote the hydrolysis of exchangeable Aland release lmoton,and result in drop in the pH of the system.There might be calcium phosphates formation in soils with P addition n 0.01 mol CaCl₂ when pH>6,causing the equilibriatrn concentration of P to decrease markedly.Organic matter had an important effect on P sorption by soils.At iow pH,organic matter might inhibit the hydyolysis of Al⁸⁺ in solution through Al-organci complex formation.Mceanwhile,the organci anions might compete with phosphate for reaction sires on the surface of hydroxy-Al species.Both of the mechanisms meantioned above leaded to the decrease of P sorption in a cidic soils.