Humus characteristics after maize residues degradation in soil amended with different copper concentrations

Crop residues humification is an important process in nutrient cycling in agroecosystems. A preliminary laboratory incubation experiment of 180 days was conducted to evaluate the quantitative and qualitative characteristics of humic fractions formed during the humification process of maize residues in soil amended with different copper (Cu) concentrations. The Cu concentrations tested were 0, 50, 100, 200, 400, 600, 800, and 1000 mg Cu/kg dry soil. Results showed that the carbon content of humic fractions, i.e. humic acid (Ha) and fulvic acid (Fa), increased with the increase of Cu concentrations; the exception was carbon content of HA that initially decreased at the concentration of 50 mg Cu/kg. The color coefficient (AlogK) and activation degree (AD) of HA increased with increasing Cu concentrations while the relative color intensity (RF) decreased. In summary, we found that the carbon accumulation of humic fractions increases while the degrees of humification and aromaticity of HA decrease with increasing Cu concentrations in soil.