Land Use Effects on Soil Organic Carbon Index and Nitrogen Pools of a Tropical Coastal Plain Sands in Southern Nigeria

Land use types can of considerable interest in efforts to quantify soil organic C and nitrogen (N) cycling, both of which are important for soil stability and fertility. A study was carried out on a tropical rainforest soils in southern Nigeria to quantify soil organic carbon and nitrogen pools and other indices under forested, 5-year fallow, cocoa plantation and a 5-year continuous cassava land uses. Soil samples were collected at 0-15 cm and 15-30 cm depths for measurement of these indices. Results revealed that total organic carbon (TOC and total nitrogen (TN) varied significantly among the different land uses. TOC of 30.2 g kg-1 was higher (p<0.05) in forested soils at in the 0-15 cm top soil and 22.3 g kg-1 in the subsoil. Total N was statistically significant (p<0.05) at 2.61 and 2.01 in forested and 5-year fallowed soils, respectively. The carbon pool index (CPI) was significant at 1.63 in forested soils, while nitrogen pool index (NPI) 1.30 in similar soil (p<0.05) in 0-15 cm topsoil. In 15-30 cm subsoil, CPI and NPI values were in the order of forested > cocoa plantation > 5-year cassava cultivation, with the least values of 0.44 CPI and 0.35 NPI found in 5-year cassava plots. It was concluded that CPI and NPI are valuable indicators for analyzing changes in soil quality induced by maintaining a 5-year fallow. It was found that forested and 5-year fallow land uses can be used to improved C and N stock, as well as the structural and hydraulic properties of the soils.