Influence of Fallow Ages on Soil Properties at the Forest-Savanna Boundary in South Western Nigeria

Aims: This study examined changes in soil properties under different fallow ages within the forest-savanna boundary in southwest Nigeria.

Study Design: The study area was covered with grid lines of 2 km2 with numbered quadrants. Ten quadrants were randomly selected as sampling sites, from each quadrant, six different fallow plots of varying ages were selected to make up 60 plots of 40 m by 25 m each.

Place and Duration of Study: The research was conducted at Ekiti North local government areas (LGA) of Ekiti State in 2014.

Methodology: Soil samples (0-15 cm) were collected from soils of different fallow ages (1, 2, 4, 5, 6, 8, 10, 15 and 20 years) and analysed for organic matter, pH, available P, exchangeable cations, nitrate-nitrogen, sand, silt, clay and soil moisture using standard methods.

Results: Most of the examined soil properties increased gradually with increase in fallow age. Significant correlation (r2 = 0.25) was obtained between soil pH and age of fallow in the forest zone. Significant correlation (r2 = 0.01) was obtained between age of fallow and organic matter for both forest and savanna zones thus indicating increase in soil organic matter as fallow age increases. Soils of the forest fallows were more fertile than soils of the savanna. Forest sand decreased with fallow age while there was substantial degradation of clay particles in the savanna.

Conclusion: Late and unmonitored burning system in the savanna fallow should be discouraged. Following the rate of depletion of soil properties due to cultivation and shortening of fallow age, other sustainable options as suggested in this work would help maintain soil fertility.