Based on soil carbon saturation capacity what is the potential for soil carbon improvement in rice-based cropping systems of northwest region of Bangladesh?

Abstract

The regional study determined soil organic carbon (SOC) saturation capacity and deficit of rice-based cropping systems (RBCS) in a range of land resource, crop and management combinations to identify which RBCS had the greatest potential for improving SOC. Six RBCS were examined and the crop-diversified and mustard-rice triple cropping systems in medium highland (MHL) had the greatest potential with the highest carbon saturation capacity and lowest carbon deficit. This finding was largely attributed to the location of these RBCS where the soil's dominant clay mineral types (1:1 or 2:1 clays) and level of inundation resulted in a higher proportion of fine soil particles compared to the other RBCS. Higher SOC levels recorded in these systems, hence the lower soil carbon deficit, was also partly due to greater carbon inputs from three annual crops and greater retention of crop residue. In contrast, maize-rice, wheat-rice, and vegetable-rice triple cropping systems on highland (HL) had less potential for soil carbon improvement. The location of these RBCS in HL areas, which are prone to SOC loss through soil erosion, combined with less crop diversity, low crop residue retention and greater soil disturbance through tillage further reduces the likelihood of SOC increases. Largely due to these management factors the most vulnerable RBCS is rice-rice double cropping system on MHL, which has a 76 % deficit to carbon saturation capacity, despite a more favorable land resource. To address soil carbon deficits, especially under vulnerable soil types, various management strategies could be applied, including: optimal fertilization, use of organic manures, crop rotations, and greater crop residue retention. Enhancing soil resilience is crucial for maintaining productivity, especially in high tillage systems. Greater crop diversity and increased residue retention could improve carbon sequestration, benefiting soil health and climate change mitigation. Promoting crop-diversified and mustard-rice systems among smallholder farmers in suitable regions of the Floodplain and Terrace soil physiography throughout Bangladesh, is recommended, while other systems with higher soil carbon deficits require increased carbon inputs, by reducing fallow periods and crop residue removal in the region. Support for smallholders through access to land of greater land capability, subsidized inputs, and agricultural extension activities is essential for enhancing soil resilience and productivity in RBCS.