Migration of Copper with Wheat Straw in Soil under the Alternate Dry-Wet and Eluviation Conditions

The migration of heavy metals in soil relates to the soil type and cultivation practices. It is necessary to examine the migration changes of heavy metal under the specific areas of concern. Straw returning to the field is one essence of traditional agriculture; the migration of copper (Cu) in agricultural soil of Henan province, China, with and without wheat straw under alternate dry-wet and eluviation conditions was studied in this paper. Experiments examined the morphological changes of Cu among different bound fractions of exchangeable (EXC), carbonate (CAR), iron and manganese oxide (OX), organic matter (OM), and residual (RES) under different conditions. Results showed along with the addition of wheat straw in the soil, the CAR and OX fractions decreased while the OM and RES fractions increased, at the same time, the EXC fractions decreased at high Cu concentration and increased at low Cu concentration. In addition, the EXC and CAR fractions of Cu increased and the RES fractions decreased when the Cu concentration rose under dry-wet alternate conditions. In the eluviation experiment, the release amount and rate of Cu improved along with the addition of wheat straw. Although wheat straw could make the distribution of Cu turn into the more stable fractions such as RES, the heavy metal was unstable and much easier to dissolve into the leaching water in the course of heavy metal migration. According to the results, it was suggested the wheat straw returning to the field should comprehensively consider the local conditions.