Effects of Chinese Milk Vetch and Rice Straw on the Soil Nutrients and the Copper Forms

  Objective  The effects of Chinese milk vetch (Astragalus sinicus L.) and rice straw on the availability and the forms of copper (Cu) were studied in order to afford the theoretical support for the remediation of slight Cu contaminated paddy soil by the addition of Chinese milk vetch and rice straw.

  Method  An in-lab experiment was conducted with five treatments: control (CK), rice straw (R), Chinese milk vetch only (G), Chinese milk vetch and rice straw with the mass ratio 3∶1 (R3G1), and the mass ratio 1∶1 (R1G1).

  Result  The results were shown that the application of Chinese milk vetch and rice straw enhanced the soil fertility significantly. The total nitrogen (N) and available phosphorus (P) of G treatment were increased by 26.92% and 11.46%, respectively. The contents of dissolved organic N (DON) of G treatment were increased by 8.40% and 20.47% than those of R3G1 and R1G1, respectively. The dissolved organic carbon (DOC) of R3G1 was higher by 32.81% and 15.94% than that of the treatments of R and G, respectively. All of the addition of Chinese milk vetch or/and rice straw decreased the content of the available Cu by 28.46% ~ 51.03% significantly. The available Cu were decreased with the increase of relative amount of rice straw. The contents of acid-extractable Cu were deceased by 15.45% ~ 23.19% and the contents of residual Cu were increased by 6.08% ~ 11.39% with the addition of Chinese milk vetch and rice straw compared with CK. The content of the residual Cu of R3G1 was higher than of G and R1G1 by 4.98% ~ 5.01% and the increase of relative amount of rice straw increased the content of the residual Cu. There were significant negative correlation among DOP, DON and the available Cu and the acid-extractable Cu. The amount of explanations of DOP and DON for the availability and the forms of Cu were 61.5% and 23.3%, respectively.

  Conclusion  In conclusion, the paddy soil fertility was improved with the application of Chinese milk vetch and/or rice straw. The availability and the forms of Cu were influenced by DOP and DON. The mass ratio of rice straw and Chinese milk vetch with 3∶1 had better effects on the stability of Cu.