Impact of agricultural practices on soil organic carbon stock in the foreke-dschang escarpment (Cameroon western highlands)

The soils of the Foreke-Dschang escarpment are very fragile and prone to erosion and landslides. These soils are under intense demographic pressure with the heavy conversion of forest into agroforestry systems. This work aims to highlight both the positive and negative effects of agricultural practices on the soil organic carbon stock (SOCS) of the Dschang-Foreke escarpment and to propose suitable conservation measures. Soil samples were taken from different agroforestry systems and analysed in the laboratory for physic-chemical characteristics by standard procedures. The main results revealed that the organic matter content is higher (2.45±1.70%) in the foot slope (BP) than in the upslope (SP) (2.16±0.78%), midslope (MP) (1.85±0.45%), upslope forest soils (PFCS) (1.58±0.18%) and Disturbed soil samples for midslopeforest soils (PFCM) (1.20±0.90%). The SOCS in agroforestry soils are higher in BP (42.55±6.13 t/ha) than in MP (21.02±5.48 t/ha) and SP (2.15±1.39 t/ha) as well as the C/N ratio (18.45, 11.12 and 1.91). BP soils have relatively higher humin (6.57±4.60% DM) and C/N ratio (18.45), but lowerfulvic acid-to-humic acid (AF/AH) ratio (0.38) and low soil structural instability index (SI) (1.76±0.56). This might justify the structural stability of soils in this topographic position. In forest zones, although the SOCS is higher at the top (33.16±5.79t/ha) than in MP (19.70±6.76t/ha) as well as the C/ N ratio (20.03 and 8.72). Forest soils in MP were structurally more stable thanks to their low AF/AH ratio (0.58) and low structural instability index (6.07±1.87t/ha). Only the reconversion of the forest into lowland crop plots would have better stored carbon. To improve the structural stability of soils in MP and SP, the contribution of compost or biochar and poultry manure is strongly recommended.