Determining the role of land resource, cropping and management practices in soil organic carbon status of rice-based cropping systems

Rice-based cropping systems (RBCS) cover the majority of cultivated land in Bangladesh and are the country's primary source of food security. To bolster food security, cropping intensity has increased by 192% in the last 30 years. Concerns have been raised about the sustainability of such cropping increases, particularly for soil pro-ductivity and resilience, with many areas reporting low soil organic carbon (SOC). The research assessed the levels of SOC, total nitrogen (TN) and soil pH in RBCS to identify relative importance of the land resource, cropping and management settings on these soil properties and to determine options for sustainable land use intensification. Soil samples (0-30 cm) were collected following stratified random design from a range of RBCS and analyzed for SOC, TN and soil pH. These soil properties were interpreted against previously developed farming system typology of Soil Carbon Improvement Likelihood (SCIL) and the legacy soil datasets. SOC was recorded higher in the stop-go triple cropping (12.00-16.33 g/kg) compared to the triple and double cropping intensities (6.90-8.30 g/kg). The crop-diversified and mustard-rice cropping systems of High SCIL, where there is crop rotational diversity and high residue retention, recorded a higher SOC. However these systems were also located on inherently fertile soil (Floodplain medium highland) compared to the less diverse cropping systems (wheat-rice, veg.-rice and rice-rice) of Medium and Low SCIL. The wheat-rice system had the lowest SOC (5.46 g/ kg), which is considered to be a consequence of low crop residue retention and reduced periods of inundation in highland on the Piedmont plain or Terrace. However, the build up of SOC and TN was linked to soil acidification associated with altered fertilizer regime and crop residue removal. Cropping intensity, and in particular, the associated cropping systems and management, were determinants of SOC, depending on which land resource setting and cropping systems were practiced by the smallholders. The types of cropping systems and management options in land resource settings were identified that have the potential for sustainable land use intensification. The implications would be to ensure these cropping systems are conserved, and trade offs contemplated to meet the rising food demand and carbon sequestration goals to counteract smallholder vulnerability to climate change in Bangladesh and South Asian countries.