ABSTRACT

Soil samples were taken from a cocoa plantation treated with Bordeaux mixture at Ajata Bende to evaluate various copper forms. Copper forms extracted were total, available, water soluble, exchangeable, organic matter, manganese oxide, amorphous iron oxide, crystalline iron oxide and residual fractions. The study was conducted as a single factor experiment in randomized complete block design (RCBD). The study area was partitioned into five equal blocks. Sixty percent of each block was randomly sampled for soil at depths: 0-15cm (surface soil), 15-30cm (subsoil A) and 30-45cm (subsoil B). A total of forty five auger samples were collected during the dry and wet season respectively to determine seasonal effect on parameter measured. Results of analysis showed that Cu concentrations in the soil were affected by the application of Bordeaux mixture, and by seasonal variations. The surface soil had the highest level (66.29mgkg4) of total Cu form whereas the subsurface soil B had the lowest value (23.52mgkg of total Cu form in the wet season. The surface soil recorded the highest level ( 26.93mgkg-1) of available Cu form while the subsurface soil B had the least (6.62mgkg-1) value of available Cu form in the wet season. The surface soil and subsurface B had the highest (35.06mgkg-1) and least (12.94mgkg'1) value of total Cu form during the dry season. The highest level of available Cu form of 14.00mgkg1 and the least value of 3.04mgkg‘:l were observed in the surface and subsurface soil B, respectively during the dry season. The levels of total and available Cu in the soil were higher in the surface soil and in the wet season than in the subsurface soil and in the dry season. Statistically, the study indicated that both the total and available copper forms of the surface soil differed significantly (P

<0.05) from those of the subsurface soils. Also, total and available Cu forms of the soil in the wet season differed significantly (P><0.05) from those of the dry season. A sequential extraction technique used to characterize bonding of Cu to the soil showed that the exchangeable and Mn oxide fractions had the least and highest Cu level of 0.48% and 31.55%, respectively in the wet season and 0.35% and 37.66% in the dry season. The highest Cu level was observed in the Mn oxide fraction during the dry season. Seasonal variation had no effect on water soluble, exchangeable and residual Cu fractions but greatly influenced the organic matter, Mn oxide, amorphous Fe oxide and crystalline Fe oxide forms. Manganese oxide and amorphous Fe oxide forms of Cu were 14.43mgkg1 and 11.74mgkg1 respectively in the wet season, and 25.08mgkg’1 and 16.97mgkg1 respectively during the dry season; they served as sink for Cu. The result of this study will serve as a guide in the adoption of appropriate soil management techniques and amendments that will regulate Cu mobility in the soil and plant availability of Cu. This will reduce the risk of contamination of food chain and underground aquifer.>