Transformation of Copper in Two Soils as Influenced by Phosphorus Application

A pot study was carried out to study the effect of P application on transformation of Cu in a calcareous loamy sand (0.13% CaCO₃, Typic Ustipsamment) and non-calcareous sandy loam (Typic Haplustept). Treatments consisted of six levels of P (0, 25, 50, 100, 200, and 400 mg P kg⁻¹ soil) as monocalcium phosphate monohydrate and four levels of Cu (0, 5, 10 and 20 mg Cu kg⁻¹ soil) as Cu-EDTA in all possible combinations applied to wheat with three replications. Soil samples were analysed for various chemical pools of Cu. In calcareous soil, P application decreased exchangeable and specifically adsorbed Cu but increased carbonate bound-Cu. However, in non-calcareous soil, applied P decreased the content of Cu in exchangeable, amorphous and crystalline oxides but increased the organically bound Cu. A major portion (43–45%) of the added Cu entered into residual mineral fraction followed by amorphous oxides (32–34%) and crystalline oxides (7.1–12.7%) in both the soils. Only 3.27 and 2.93% of applied Cu at 20 mg kg⁻¹ soil in calcareous and 2.81 and 1.44% in non-calcareous soil entered into plant available exchangeable and specifically adsorbed fractions, respectively.