Molybdate sorption-desorption in soils treated with phosphate

• Published in: Geoderma Vol. 48; no. 3; pp. 321 - 333
• Main Authors: Xie, R.J., MacKenzie, A.F.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.1991
• Subjects: FOSFATOS; MOLIBDENO; MOLYBDENE; MOLYBDENUM; PHOSPHATE; PHOSPHATES; SOIL SOLUTION; SOIL SORPTION; SOLUCIONES DEL SUELO; SOLUTION DU SOL; SORCION DEL SUELO; SORPTION DU SOL
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/0016-7061(91)90051-T

Molybdenum availability in soils may be altered with P additions. Sorption-desorption of Mo as a function of added P was studied in two soils, a Dalhousie (Humic-gleysol) clay and a St. Bernard (Eutric-cambisol) loam. The soil samples were shaken with solutions containing varying amounts of phosphates and molybdates in 0.03 M KClO 4. The first equilibration measured P sorption, the second Mo sorption and P desorption, and the third Mo desorption and further P desorption. Each equilibration was carried out for 72 h. Initial pH of the solutions was held at 6.0. Sorbed P reduced Mo sorption, especially at high P addition levels. Of the Freundlich, Langmuir, Gunary and Temkin isotherms, the experimental data fitted the Temkin isotherm best. The presence of P reduced the intercept values of the Temkin equation, indicating a reduced affinity of surfaces for Mo. In the presence of various amounts of sorbed P, Mo sorption was described best by Gunary isotherms that included a P term ( itr 2 > 0.93, P < 0.0001). In the Dalhousie clay soil, a quadratic effect of sorbed Mo on desorption of Mo was noted. Higher levels of P addition resulted in relatively more Mo desorption, although the absolute amount of desorbed Mo was decreased because of the reduced initial Mo sorption. In the St. Bernard loam soil, P additions increased Mo desorption at any given level of Mo sorption.