Dynamics of humic substance complexed copper and its relationship to copper leaching during composting of chicken manure

Changes of humic substances and their complexed copper during composting of chicken manure with different extractants of H2O, NaOH and NaOH-Na4P2O7 was studied, and leaching experiment was conducted to investigate the dynamics of copper leaching and its relationship to humic substances complexed copper(HS-Cu). The results showed that NaOH-Na4P2O7 extractable HS-Cu was the highest among three extractants of NaOH-Na4P2O7, NaOH and H2O, and the average amount of extractable HS-Cu was 46.8%, 34.5% and 6% of total copper, respectively. During the decomposing process, NaOH-Na4P2O7 extractable HS-Cu increased with decaying time. NaOH extractable HS-Cu also increased in the period of decaying for 50 days, and after that time there was no significant change. H2O extractable HS-Cu increased in the period of decaying for 21 days and then decreased. For the NaOH-Na4P2O7 extractable HS-Cu, humic acid complexed copper (HA-Cu) was the main form, but for the H2O extractable HS-Cu, the fulvic acid complexed copper (FA-Cu) was main form. For the NaOH extractable HS-Cu, FA-Cu was main form before decaying for 50 days, and after that time, HA-Cu was main form. Copper leaching increased with the decomposing process before decaying for 50 days and then decreased. The average amount of leaching copper was about 20 percent of total copper, which was correlated to NaOH or H2O extractable HS-Cu and organic carbon, but was not correlated to NaOH-Na4P2O7 extractable HS-Cu.