Factors influencing phosphorus adsorption in mine soils in Galicia, Spain

Available phosphorus levels and P sorption capacity were investigated in soils derived from coal mine spoils at As Pontes (Galicia, NW Spain), currently in the process of reclamation. Clays and shales, often in conjunction with pyrite and other sulphides, are the main constituents of the spoils; many are extremely acid as a result of oxidation of sulphides. Reclamation tasks consisted of topsoiling, chemical and organic fertilizing or various amendments. Two depths (0-15 and 15-30 cm) were sampled and analysed at each sampling site. In total, 140 samples were collected ranging in pH-H2O from 2.7 to 8.4. Olsen P values ranged between 1 and 54 mg . kg(-1). The phosphorus sorption index (PSI), determined according to Bache and Williams (1971), ranged between 2.4 and 55.1. Multiple correlation between PSI and several soil parameters was investigated using a stepwise linear regression method. Four soil parameters (oxalate-extractable Fe and Al, pH in KCl and organic carbon) were shown to explain 79% of the variance in log PSI. The correlation equation found was: log PSI = 3.562 + 0.519 x log(Al + Fe)(o) - 0.065 x pH-KCl + 0.247 x log(org. C).