Effect of organic materials on soil microbial biomass carbon

A laboratory study was conducted at Bangabandhu Sheikh Mujibur RahmanAgricultural University, Bangladesh during 1997. The changes in microbialbiomass carbon due to incorporation of different organic materials in soil werestudied to determine the contribution of microbial biomass C to carbon pool ofsoil. The organic materials incorporated into the soil were; rice straw, wheatstraw, Napier, azolla, water hyacinth and town refuse. Individual organicmaterials were incorporated in the soil immediately after soil moistureadjustment (50% of maximum water holding capacity) at the rate of 150 mg/20g air dried soil and were incubated for 98 days. The C account in the form ofCO2 (CO2-C) was measured up to 98 days at different time intervals. All thesoil samples incorporated with different sources of organic matter showedhigher biomass C as compared to untreated soils. At 98 days of incubation,wheat straw treated soil gave higher CO2-C (133.93 mg/100 g air dry soil) andbiomass C (215.31 mg/100 g air dry soil) followed by town refuse treated soil(CO2-C 123/61 mg/100 g air dry and biomass C 192.37 mg/100 g air dry soil).The amounts of CO2-C and biomass C recorded at 7 days of incubationgradually increased in soil treated with all the organic materials up to 98 daysof incubation but the amounts varied with respect to different organicmaterials. Maximum CO2-C and biomass C were produced at the primary stageof incubation (7 to 21 days). With the increase of incubation period, CO2-C andbiomass C production rates were decreased. Contribution of biomass C toorganic C was higher in the soil treated with Napier (1.81%) followed by thesoil treated with town refuse (1.58%). It was concluded that among organicmatter sources wheat straw had greater ability to increase CO2-C and biomassC.