ORGANIC CARBON SEQUESTRATION AND SELECTED SOIL PHYSICAL PROPERTIES AT TWO DEPTHS WITHIN DIFFERENT LANDUSE TYPES IN SOUTHWESTERN NIGERIA

The study was desiqned to show interaction between organic carbon dynamics and soil physical properties at two depths within different landuse. The two landuse are: continuous maize (CM) field which had been cultivated by farmers for 15 years and a planted Gliricidia sepium fallow (GF) adjacent 15 years fallow field. The mean values of organic carbon stock were 2.59 Mg ha -1 for continuous maize plot and 5.0 Mg ha -1 for Gliricidia sepium fallow with a significant different at P ≤ 0.05. Continuous maize plot had higher bulk density at 0 - 0.1m depth (1.53g cm -3 ) than Gliricidia sepium fallow plot (1.25 g cm -3 ). Continuous maize plot had higher bulk density at 0 – 10cm depth (1.53g cm -3 ) than Gliricidia sepium fallow plot (1.25 g cm -3 ). The soil moisture content at various times and different depths generally showed the following trend: CM < GF (P ≥ 0.05). The mean values were 0.476g/g (CM) and 0.621 g/g (GF) at 0 – 10cm depth. At 10 – 20 cm depth, the values were 0.404 g/g (CM) and 0.591 g/g (GF) and finally at depth 20 – 30 cm, the values were 0.364 g/g (CM) and 0.550 g/g. The result also show a significantly higher value of saturated hydraulic conductivity in Gliricidia sepium Fallow plot (0.12mm s -1 ) compared to continuous maize plot (0.104 mm s -1 ). Gliricidia sepium fallow plot had higher equilibrium infiltration rate (0.103 mm s -1 ) than continuous maize plot (0.015mm s -1 ). The high organic carbon in planted fallow of Gliricidia sepium impact positively on the soil physical properties studied and revealed how continuous cultivation planting maize was deleterious to soil organic carbon accumulation.