Variation in Total Soil Organic Carbon Stocks in Relation to Some Land Use Systems in the Bamenda Highlands, Cameroon

Climate change and food security are among the pressing challenges facing humanity in the 21st century. Soil organic carbon (SOC) stocks, total nitrogen (TN), texture, and bulk density (BD) are important soil properties, which control climate change. Three land use systems (smallholder farmlands, grazing lands, and forest lands) that coexist in the Bamenda Highlands (BH) influence ecosystem services and induce soil degradation with the loss of SOC. The objective of this study was to evaluate the variation of SOC and some soil physicochemical properties as affected by the three land use systems (LUS). A total of 21 composite soil samples collected from 7 microclimatic zones of BH following “S” shape plots to the depth of 0 - 30 cm, were analysed for moisture content (MC), SOC, TN, BD, available phosphorus (Av.P), pH and texture. The results revealed that grazing land had the lowest mean sand content (40.79 ± 4.07). Mean MC, TN and SOC (%) content were significantly higher (p < 0.05) in forest land than those in the grazing land and smallholder farmlands. Conversely, BD and Av.P were significantly higher (p < 0.05) in smallholder farmlands than grazing and forest lands probably due to different litter accumulation and agricultural practices. Moisture content and TN revealed positive significant correlations (p < 0.05) with SOC, while BD and Av.P revealed negative significant correlations (p < 0.05). Mean SOC density in smallholder farmlands (132.91 ± 9.48 tC/ha) was the lowest among the three land use types. Losses in CO2 equivalence, as a result of land use change from forest lands to smallholder farmlands were 137.33 t/ha while that from grazing lands to smallholder farmlands were 109.13 t/ha. Total organic carbon (TOC) stocks differed significantly (p < 0.05) from smallholder farmlands (10.73 Mt) to forest lands (91.13 Mt). A sustainable farming technique that enhances SOC sequestration and minimizes soil CO2 emissions is therefore recommended to replace tillage ridges formation commonly practiced by smallholder farmers.