Effects of land use on Soil Organic Carbon fractions in soils of Njala Landscape in Sierra Leone

Abstract

─ Soil organic carbon fractions reflect the difference in soil organic carbon from one land use to another, and it can be regarded as an indication of the degree of soil organic carbon deterioration or improvement.Although knowledge of importance soil quality indicators is vital for replenishing and maintaining soil fertility, little information is available on the effect of different land use management on soil organic matter fractions in Sierra Leone.In the present study, the effects of different land use on the distribution of soil organic matter fractions in soils of the Njala series was assessed.The study revealed both positive and negative effect of land uses on Organic carbon fractions at the Matturie site showed an increase upon conversion of grassland to tree cropping except for carbon in the silt+clay fraction.The total organic carbon, light fraction carbon and particulate organic carbon fractions were significantly greater in the forest soil than in soils under grassland.The decline in the silt+clay fraction organic carbon was an indication that residue decomposition and organic matter addition are low in this area.At the Old Agronomy Site, where Acacia and Gliricidia fallows were converted to agriculture (groundnut), soil organic carbon (SOC) contents showed a decrease under annual cropping land use types.The conversion of Acacia and Gliricidia land use to groundnut cultivation resulted in loss of total organic carbon and all carbon fractions.The largest decline was in the light fraction carbon (16.46%)., followed by the particulate organic carbon (15.82%), total organic carbon (14.63%) and the silt+clay fraction (5.83%).The least decline occurring in the silt+clay fraction indicates that organic matter is better protected in silt+clay fraction.Similar changes in soil organic carbon fractions, as observed for the Old Agronomy site, were observed at the NATC site.The results showed that there are greater losses of particulate organic carbon (17.24%), light fractions (18%) and total organic carbon (16.21) than from the silt+clay fraction (7.34) when the land use is changed from secondary forest to arable cropping.