A study of copper sorption in soils as influenced by soil characteristics using a laboratory column leaching technique

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Copper (Cu) is essential to plant metabolism, but when present in bioavailable forms at excessive levels, has the potential to become toxic to plants. It is frequently measured for regulatory decision making on toxicity levels in soils. Decisions on the utilization or containment of potential Cu toxicity require an understanding of its behaviour in the soil. Two experiments arranged in a Randomized Complete Block Design (RCBD), with four replications each, were therefore carried out separately, to assess the distribution of Cu in the soil as affected by selected soil characteristics. The treatments were 0.00, 12.33, 18.50 and 24.70 g/m2 Nordox powder per column with an area of 81.04 cm2. Two different soils, Nta and Temang soil series, (Gleyic Arenosol and Eutric Dysteric Gleysol, respectively.) made up of different parent materials were used for the studies. The study showed that Cu sorption increased with increasing soil organic matter content and confirmed soil organic matter as an important accumulator of Cu. This was further supported by the positive correlation between Cu and SOM with a correlation coefficient (r2) of 0.999 and 0.996 under the Nta and Temang soil series respectively. Whilst the correlation between CEC and Cu sorption was positive in the Nta series, it was negative in the Temang series. Generally, copper sorption reduced with increasing soil depth along the soil column in both series. The increased contact time between the leaching solute and the top soil increased Cu sorption in the topsoil than the subsoil. The clay content did not show any regular pattern with Cu sorption. Copper sorption to the soil matrix increased with increasing pH in both soil types, but the effect was much more pronounced in the Nta series which generally recorded higher soil pH values than Temang series. Nta series adsorbed more Cu than the Temang series at all levels of Cu application. The increased sorption could be due to the relatively higher SOC content and pH of the Nta than Temang series. The results showed the annual Cu movement in the soil to be 4.17 and 4.58 cm y-1 for the Nta and Temang series respectively. Also, copper would require about 40 and 76 years to reach the aquifer in Nta and Temang soil series, respectively. Continuous application of Cu-based fungicides to agricultural soils containing little amounts of organic matter should be exercised with caution as its accumulation may reach toxic levels. Continuous application of Cu may equally have serious groundwater contamination implications especially under low soil reaction conditions. Industries processing heavy metals can set up large column leaching apparatus to clean industrial effluents before disposing them into the environment.  
A thesis submitted to the Department of Crop and oil Sciences, Faculty of Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, in partial fulfillment of the requirements for the award of the Degree of Master of Philosophy in Soil Science.