Seasonal Variations in Grain Yield, Greenhouse Gas Emissions and Carbon Sequestration for Maize Cultivation in Bangladesh

Rationale: Greenhouse gas (GHG) emissions from crop agriculture are of great concern in the context of changing climatic conditions; however, in most cases, data based on lifecycle assessments are not available for grain yield variations or the carbon footprint of maize. The current study aimed to determine net carbon emissions and sequestration for maize grown in Bangladesh. Methods: The static closed-chamber technique was used to determine total GHG emissions using data on GHG emissions from maize fields and secondary sources for inputs. A secondary source for regional yield data was used in the current study. GHG emission intensity is defined as the ratio of total emissions to grain yield. The net GHG emission/carbon sequestration was determined by subtracting total GHG emissions (CO2 eq.) from net primary production (NPP). Results: Grain yields varied from 1590 to 9300 kg ha(-1) in the wet season and from 680 to 11,820 kg ha(-1) in the dry season. GHG emission intensities were 0.53-2.21 and 0.37-1.70 kg CO2 eq. kg(-1) grain in the wet and dry seasons, respectively. In Bangladesh, the total estimated GHG emissions were 1.66-4.09 million tonnes (MT) CO2 eq. from 2015 to 2020, whereas the net total CO2 sequestration was 1.51-3.91 MT. The net CO2 sequestration rates were 984.3-5757.4 kg ha(-1) in the wet season and 1188.62-5757.39 kg ha(-1) in the dry season. This study observed spatial variations in carbon emissions and sequestration depending on growing seasons. In the rice-maize pattern, maize sequestered about 1.23 MT CO2 eq. per year(-1), but rice emitted about 0.16 MT CO2 eq. per year(-1). This study showed potential spatiotemporal variations in carbon footprints. Recommendation: Special care is needed to improve maize grain yields in the wet season. Fertiliser and water use efficiencies need to be improved to minimise GHG emissions under changing climatic conditions. Efforts to increase the area under cultivation with rice-maize or other non-rice crop-based cropping systems are needed to augment CO2 sequestration. The generation of a regional data bank on carbon footprints would be beneficial for combating the impact of climate change.