The effect of moisture content on the release of organic matter and copper to soil solutions

The effect of moisture content on the concentrations of dissolved organic matter (DOM), dissolved copper, Cu2+ activity, and pH of soil solution was studied on 7 soils in the range of moisture content from 1.5 to 10 g water per gram soil. An increase in moisture content resulted in a decrease in DOM concentration which followed the desorption isotherm equation. Copper concentration decreased with the increase of moisture content but this did not influence Cu2+ activity (pCu) in soil solutions of the soils with pH < 6.4. In the soils with pH ≥ 6.4 both pCu and pH at low moisture content differed from those observed in soil suspensions. This may indicate that pCu in soil solutions of acid soils is controlled by equilibrium with Cu sorbed by soil organic matter while in soils with pH ≥ 6.4 by equilibrium with Cu retained on calcium carbonate. The increase in dissolved Cu correlated (R2 = 0.60 to 0.98) with the increase in DOM concentration.