The pH effect on sdrption‐desorption and fractions of zinc in phosphate treated soils

Zinc sorption‐desorption and Zn fractions in three soils, a Dalhousie clay (DT: Eutric Brunisol), a St Bernard loam (ST: Melanic Brunisol) and an Uplands sand (UT: Ferro‐Humic Podzol), were studied with and without added P at different pH values. Phosphate addition increased Zn sorption (Zns) in the order: DT clay > ST loam > UT sand. A positive correlation was noted between Zns and pH for soils treated with and without P. Phosphate addition reduced Zn desorption (ZnD) especially at low pH and was attributed to P induced pH effect. At high pH values, the P effect was less important. An increase in pH value resulted in less 0.5 M KNO3‐extractable Zn (ZnKNO3) and more 0.5 NaOH‐Zn (ZnNaOH) and HNO3 extractable Zn (ZnHNO3). Compared with zero P treatments, P addition reduced ZnKNO3 at low pH value but increased ZnNaOH at all pH values.