Impact of land use on carbon sequestration potential of soils in Agroecological Zone-9 of Bangladesh

This study aimed to ascertain the effect of land uses (cropland, orchard, grassland, and fallow) on soil OC pools in two depths (0–10 and 40–50 cm). Particulate organic matter (POM) (> 53 µm) and mineral associated OM (MOM) (< 53 µm) pools were physically separated from bulk soils and analyzed for OC and N analysis. For both depths, the soil from grassland showed considerably higher OC (0.96-1.47%) and N (0.084-0.095%) values than the other land uses. In surface depth, the lowest OC was found in cropland soil (0.83%) and in sub-surface, it was in fallow land soil (0.75%), whereas the orchard soil had moderate OC in both depths. Depth showed significant differences in OC distribution. Surface soils had higher OC than the sub-surface soils which can be explained by the continuous addition of organic residues (crop/leaf/dried grasses) on the top soil. The distribution of POM and MOM fractions among the soils of different land uses were different. Interestingly, cropland and orchard soils had higher MOM-OC (MOC) than POM-OC (POC) in comparison to the relatively less disturbed grassland and fallow land soils. The amount of OC and N in OM pools was significantly different among the land uses in both depths. In surface depth, cropland soil showed the lowest POC content whereas the orchard and fallow land soils showed relatively higher. The MOC content was highest in fallow land (2.73%), lowest in orchard (1.30%) and cropland had moderate amount. In sub-surface depth, amount of OC was higher than surface soils and the trend of OC distribution between POM and MOM was different. Grassland soil had the highest OC (2.89-3.10%) for both fractions, followed by cropland > orchard > fallow. These findings showed that in cropland disturbance in soil could aid in depleting OC only from the most labile POM pool keeping the OC almost intact in stable MOM pool. Less disturbance in native soil condition such as grassland does not always benefit in enhancing/maintaining OC, rather it depends on the quality and quantity of OM added in the soils from the vegetation cover.