A thesis submitted in partial fulfillment of the requirements for the degree of Master in Natural Resources Management, School of Environment, Resources and Development

Thesis (M. Sc.) - Asian Institute of Technology, 2012

Sequestering carbon in soil aggregates is a long term solution to global warming that will keep CO 2 out of the atmosphere. It is well known that substantial Soil Organic Carbon (SOC) losses occur from cultivated agricultural soils and that SOC levels are influenced by soil texture and soil aggregate stability. Soil aggregate st ability has been recognized as one of standard features of soil quality, sensitive to land management practices, as well as relating to erosion and carbon dyna mics . The study was conducted to investigate the state of carbon sequestration in soil aggregates under different cropping patterns of Khulna region. Ten different cropping patterns were selected. Soil particle size distribution, micro aggregate analysis, aggregate stability, normalized stability index (NSI) and organic carbon associated with soil ag gregates were determined. The soil organic carbon (SOC) associated with aggregate size ranges (8 - 2, 2 - 0.25 and 0.25 - 0.05 mm) were separated and determined. The % SOC associated with 2 - 0.25 mm aggregates was generally higher than % SOC associated with 8 - 2 mm and 0.25 - 0.05 mm aggregates. The state of aggregation (8.96%) and degree of aggregation (13.04%) was found high under Fallow - Fallow - T.rice cropping pattern and low under Fallow - Sweet gourd - T.rice cropping pattern. The dispersion factor (33.33%) was highest under Vegetable - Sugarcane cropping pattern. The highest NSI value (0.82) was under Fallow - Fallow - T.rice cropping pattern in clay loam soil. The lowest value (0.25) was under Shrimp - T.rice cropping pattern. The highest organic c arbon content in aggregate size ranging from 8 - 2, 2 - 0.25 and 0.25 - 0.05 mm was found 2.01, 2.85 and 2.83%, respectively under Fallow - Fallow - T.rice cropping pattern. The lowest organic carbon content was found 1.10, 1.27 and 1. 23%, respectively under Mustard - Fallow - T.rrice cropping pattern. The percentage of SOC associated with 2 - 0.25 and 0.25 - 0.05 mm aggregates increased with increasing clay contents of the investigated soils.