Bioavailability and form tendency of Cu and Zn in farmland soils after application of different organic fertilizers

【Objectives】 The application of livestock and poultry manure is one of the most important causes of heavy metal contamination in agricultural soils in China. In this paper, two kinds of typical livestock and poultry manure from large-scale farms were applied to soils for 1 year to investigate the bioavailability and form transformation of Cu and Zn in calcareous soil and acid soil. The results will provide theoretical basis for evaluating the environmental behavior and ecological risk of heavy metals in livestock and poultry manure. 【Methods】 A soil incubation experiment was conducted with calcareous soil and acid soil under greenhouse condition for 1 year. Nine treatments were designed: control(CK), 2% chicken manure(CM2%), 5% chicken manure(CM5%), equivalent inorganic Cu or Zn salt solutions with CM2% and CM5%(CS2%, CS5% respectively), 2% pig manure(PM2%), 5% pig manure(PM5%), equivalent inorganic Cu or Zn salt solutions with PM2% and PM5% (PS2%, PS5% respectively). Soil pH, EDTA extractable Cu and Zn contents, different forms of Cu and Zn contents were determined, and the bioavailability and form transformation of Cu and Zn from livestock and poultry manure were analyzed. 【Results】 The pH value decreased in calcareous soil but increased in acid soil after the application of chicken and pig manure, and the pH value of calcareous soil decreased 0.23 units while that of acid soil increased 0.87 units in PM5% treatment. After the application of chicken and pig manure for 1 year, the contents of available Zn in calcareous soil and the contents of available Cu and Zn in acid soil increased significantly. The available Cu increased by 1.95 times in acid soil in PM5% treatment and the contents of available Cu in CM 5% treatment were lower than those in CS5% treatment. After the application of chicken manure and equivalent inorganic salt solutions, the contents of exchangeable Cu, organic bound Cu and exchangeable Zn, carbonate bound Zn, organic bound Zn, Fe-Mn oxides bound Zn increased significantly both in calcareous soil and acid soil. And after the application of pig manure and equivalent inorganic salt solutions, the contents of exchangeable Cu, Fe-Mn oxides bound Cu, organic bound Cu and carbonate bound Zn, Fe-Mn oxides bound Zn increased significantly both in calcareous soil and acid soil. 【Conclusions】 The application of chicken and pig manure enhanced the bioavailability of Zn in calcareous soil and the bioavailability of Cu, Zn in acid soil, while the bioavailability of Cu in chicken manure was lower than equivalent inorganic salt at high dosage treatment. Cu added into both two soils through chicken and pig manure was mainly in the forms of exchangeable and organic bound form, while Zn was mainly in the forms of carbonate bound, Fe-Mn oxides bound and organic bound form. The proportions of Fe-Mn oxides bound Cu and Zn through chicken and pig manure were lower than those through equivalent inorganic salt and the proportions of exchangeable Cu and organic bound Cu were higher than those through equivalent inorganic salt in two kinds of soil. The proportion of exchangeable Zn through chicken manure was lower in acid soil while it was higher in calcareous soil than that through equivalent inorganic salt.