Effect of Soil pH, Cattle Manure and Total Copper Load on Copper Solubility in Copper Contaminated Soils

Coffee fields in Kilimanjaro, Tanzania have been contaminated with copper (Cu) as a result of long term use of Cu-based fungicides. Solubility and mobility of Cu in soils may be detrimental to the environment and human health due to possible leaching thereby contaminating underground water resources. Cu solubility and bioavailability to plants may decrease with time through conversion of the contamination to less available forms, a process referred to as 'aging'. Therefore, this study explored the interaction effects of soil pH, cattle manure and the total Cu load on Cu solubility in long term Cu contaminated soils. Soils treated with and without cattle manure were leached with water adjusted to pH levels of 4, 5, 6 or 8.5. The results revealed that Cu solubility was higher in soils with higher total Cu load and that cattle manure had varied effects on Cu solubility at different pH levels. The soils buffering capacity were adequate enough to arrest fluctuations in soils pH and therefore acid rains as well as over liming may not cause excessive solubility of Cu in long term Cu contaminated soils.