Akinbode O. A^1,, Oke D. O.², Akinbi O. J.³

This study investigated the effects of three land use management systems on the status of total and mineral-associated and particulate soil organic carbon content. The study was carried out in selected cocoa farms established within Idanre Forest Reserve, Ondo State, Nigeria. Based on the number of non-cocoa trees (shade trees) per unit area, the farms were classified into dense cocoa agroforest, sparse cocoa agroforest, and pure cocoa plantation. 3 sample plots of 25m x 25m were mapped out alternate to each other, and soil samples were collected at 5 different points along the diagonal of each plot at depths 0-15cm, 15-30cm and 30-45cm using a 3cm diameter soil auger. The results shows that surface soil (0-15cm) total organic carbon (TOC) content was highest under the sparse cocoa agroforest (5.64%) and lowest in the dense cocoa agroforest (2.86%). It was noted that sparse cocoa agroforest had potential for increasing soil organic carbon of an appreciable concentration due to the presence of few large non-cocoa trees which contributed immensely to the soil carbon stock especially through litter fall. The decreasing order for the % TOC is given as Sparse cocoa agroforest > pure cocoa plantation > dense cocoa agroforest. The result of the analysis shows a significant difference (P<0.05) in the %Particulate organic carbon (POC) and %Mineral-associated organic carbon (MOC) stored in the soil by the different land use management systems and at the different depths considered. Carbon content of MOC were higher than the POC in all land use management systems. The study concluded that soil organic carbon stored decreased with increasing soil depth across land use and sparse cocoa agroforestry with few large trees has the potentials of storing organic carbon of appreciable concentration.

land use, cocoa agroforestry, carbon fraction, mineral-associated, particulate organic carbon, Nigeria