Chemistry of Cr in some Swedish soils. 6. Native P transformation and changes in pH and cation exchange capacity in two soils incubated with potassium chromate

Abstract

Transformation of native P and changes in water pH and cation exchange capacity (CEC‐pH 7) were investigated in acid (I) and neutral (IV) soil incubated with 0, 50 and 100 mg Cr/kg for 3 months. Phosphorus was sequentially obtained as P‐resin, P‐NaHCO₃, P‐NaOH and P‐HCl, with the P‐NaHCO₃ and P‐NaOH being separated into organic and inorganic fractions. The low Cr level had little impact on the parameters. The high level increased the pH from 5.1 to 7.3 and from 6.8 to 7.5 in soils I and IV, respectively, while also significantly (P=5%) increasing CEC and decreasing P‐resin content. Subsequent to the Cr treatment, total P‐NaHCO₃ significantly declined in Soil I, but did not change markedly in Soil IV. Although total P‐NaOH was not affected by the Cr applications, its inorganic form doubled in Soil IV. Most of the total P‐NaHCO₃ and P‐NaOH was in organic form. Whereas P‐HCl was stable in Soil IV, the P nearly doubled in Soil I at the expense of P‐NaHCO₃ (r = ‐0.94**). pH was correlated with CEC (0.62*), total P‐NaHCO₃ (‐0.83**) and P‐HCl (0.76**), while CEC was correlated with P‐resin (‐0.70**), total NaHCO₃ (‐0.88**) and P‐HCl (0.94**).