Retention of Copper in Cu-Enriched Organic Soils

Copper may accumulate in organic soils in the range of 2 to 60,000 mg kg⁻¹, naturally or as a result of fertilizer or biocide applications. The authors conducted a study on Cu sorption and extraction using 28 moorsh materials varying in quality attributes. The extraction sequence included water soluble and exchangeable Cu. Sorption was described by the Langmuir equation with maximum sorption capacity (X_m) in the range of 24 to 55 g Cu kg⁻¹. The X_m was quartically related to the sum of exchangeable basic cations (SEBC) (R² = 0.97). Three sorption patterns were 138found: X_m was constant for SEBC values below 45 cmol_c kg,⁻¹ then increased in proportion of SEBC up to 85 cmol_c kg,⁻¹ and finally increased at a lower rate for higher SEBC values. The H₂O- and KNO₃-extractable Cu from added Cu at assumed toxic level (3000 mg Cu kg⁻¹) was cubically related to SEBC and pH; it was highest below a SEBC value of 45 cmol_c kg⁻¹ or a pH (0.01 M CaCl₂) value of 4.2, then declined to reach a plateau. The Cu sorption and desorption capacities in organic soils can be assessed from easily determined properties such as SEBC and pH.