Objective  The concentration of heavy metals in pig manure and its impact on the bioavailability of heavy metals in soil has long been a worldwide concern. The manure with copper (Cu) will be added to soils and the Cu fractions will be determined in soils and Chinese cabbage, in order to make sure the Cu accumulation and bioavailability.

  Methods  In this study, 1% and 3% of rotten pig manure (dry pig manure∶straw = 10∶1) were added to yellow cinnamon soil, red soil, black soil and cinnamon soil. After aging for 0, 1, 2, 3 and 5 months respectively, a pot experiment of Chinese cabbage was carried out.

  Results  The results showed that the total amount of Cu in yellow cinnamon soil, red soil, black soil and cinnamon soil increased significantly by 20.23% - 50.43%, 79.87% - 142.6%, 52.41% - 76.43% and 41.14% - 92.24% respectively. In four soils, the proportions of water-soluble Cu (F1) and carbonate-bounded form Cu (F3) increased and the increase of F1-Cu in RS-0 with 3% pig manure and F2-Cu in YCS-0 were the most significant, which was 4.55% and 16.47% respectively. The proportion of soil iron manganese oxidation form (F5) and organic-bound form (F6) Cu increased, while the concentration of residual (F7) decreased. The proportion of available Cu in soil was significantly negatively correlated with the aging time of pig manure. The proportion of available Cu in yellow cinnamon soil, black soil and cinnamon soil treated with 3% pig manure for 5 months decreased by 12.85%, 4.11% and 3.68% respectively, while that in red soil did not change significantly with the aging time. In yellow cinnamon soil, the proportion of humic acid-bound form (F4) Cu gradually increased with the extension of pig manure aging time. The application of pig manure significantly increased the Cu accumulation in cabbage, and the most significant increase was observed in red soil. The Cu contents in root and shoot increased significantly by 244.5% and 381.7% respectively, and the Cu content in shoot was 1.44-2.56 times higher than the critical value of the national food pollutant limit standard. According to the results of stepwise regression analysis equation, the contents of Cu in Chinese cabbage root system were significantly negatively correlated with soil pH, clay and F4-Cu content, but significantly positively correlated with pig manure Cu input and soil dissolve organic matter.

  Conclusion  The Cu input from pig manure significantly increases the Cu contents in soil and Chinese cabbage. The bioavailability of soil Cu is not only affected by soil properties, but also affected by pig manure itself, humic acid and dissolve organic matter in soil. By comparing different soil types, it can be concluded that the application of pig manure containing Cu stands for a relatively high risk of heavy metal pollution in the soil-crop system, especially in red soil.