Microbial biomass and its activities in salt-affected coastal soils

Seasonal fluctuations in salinity are typical in coastal soils due to the intrusion of seawater in the groundwater. We studied the effect of salinity on the microbial and biochemical parameters of the salt-affected soils of the coastal region of Bay of Bengal, Sundarbans, India. The average pH values and average organic C (OC) contents of soils from nine different sites cultivated with rice (Oryza sativa) ranged from 4.8 to 7.8 and from 5.2 to 14.1 g kg(-1), respectively. The average electrical conductivity of the saturation extract (ECe) during the summer season was about five times higher than that during the monsoon season. Within the nine sites, three soils (S-3, S-4, and S-5) were the most saline. The average microbial biomass C (MBC), average basal soil respiration (BSR), and average fluorescein diacetate hydrolyzing activity (FDHA) were lowest during the summer season, indicating a negative influence of soil salinity. About 59%, 50%, and 20% variation in MBC/OC, FDHA/OC, and BSR/MBC (metabolic quotient, qCO(2)), respectively, which are indicators of environmental stress, could be explained by the variation in ECe. The decrease in MBC and microbial activities with a rise in salinity is probably one of the reasons for the poor crop growth in salt-affected coastal soils.