Effect of Zinc and Composting Time on Dynamics of Different Soluble Copper in Chicken Manures

Chicken manures added with Cu and Zn were used for composting experiment to study the dynamics of different soluble humus complexed copper (H2O-Cu, NaOH-Cu and NaOH-Na4P2O7-Cu). The effect of zinc in compost on humus complexed copper and the relationship between humus complexed copper were also revealed. The results showed that H2O-Cu increased before the 45 d of composting and decreased thereafter. In the treatments of 1:1, 2:1 and 3:1 with the added copper content increasing, H2O-Cu increased with decomposition process. Added high level zinc in manure could decrease the relative H2O-Cu content at the last stage of composting. NaOH-Cu decreased greatly with the compost proceeding. With the added copper content increasing in manure, the percentage of NaOH-Cu to total copper decreased. Added zinc had no significant impact on NaOH-Cu concentration. NaOH-Na4P2O7-Cu increased with composting. With the added copper content increasing in compost manure, the percentage of NaOH-Na4P2O7-Cu to total copper increased, and showed an increase trend with composting proceeding. Added zinc in manure increased NaOH-Na4P2O7-Cu. In composts, 55–80% of extracted copper was present in NaOH fraction, 10–30% in NaOH-Na4P2O7-Cu fraction, and 0–10% in H2O fraction. Whatever the added copper or zinc contents increased in manures, the distribution percent of NaOH-Na4P2O7-Cu (pressed as percent of extracted Cu) increased and that of H2O-Cu and NaOH-Cu decreased. Three extracted Cu (H2O, NaOH and Na4P2O7) were strongly correlated to each other, H2O-Cu and NaOH-Na4P2O7-Cu were significantly correlated to H2O-extracted organic C and NaOH-Na4P2O7-extracted organic C, respectively.