The pH values in the profiles of unburnt (agricultural land) soils were found to increase as a function of soil depth and burning (400 to 1000℃) of the soils increased average pH by 8%. The average sand content of the burnt (soil around brick kilns) soil profiles was increased by 245%, while 39 and 36% decreased the silt and clay contents. Soil organic carbon (Corg) in the unburnt soils (0-20 cm) at different agro-ecological zones in the eastern region of Bangladesh ranged from 0.8 and 1.4%, whereas the content of microbial biomass carbon (Cmic) in the studied unburnt soils ranged between 5 and 7% of the total Corg, suggesting that the microbial biomass releasing considerable amounts of carbon in soil while burning of the soils drastically reduced this contribution to about 1%. The values of soil Cmic in the unburnt soils were approximately 2 to 6 times higher in the topsoils than the subsoils (20-60 cm). Variable rainfall, temperature and soil fertility had an overriding influence, which was reflected by the average minimum (276 μg g(-1)) and maximum (439) amounts of soil Cmic in Moulvibazar and Cox' Bazar sites. The Cmic decreased upon soil burning by 92% of its original average value (346 μg g(-1)) in the soil profile of up to 100 cm. Burning of topsoils strikingly increased the Corg/Cmic ratio by about 6 to 9 times, while reduced the C/N ratio by about 1.5 to 2.5 times. The average loss of Corg, available and total N due to burning of the soils were 66, 72 and 44% (increase over average content of unburnt soil: IOAC), respectively, which suggests that the burning of the soils offset the essential roles of soil microorganisms, reduced soil fertility and soil microbial contribution.
microbial biomass carbon
soil organic carbon
ratio of microbial biomass to organic carbon.