Soil property and microbial activity in natural salt affected soils in an alternating wet–dry tropical climate

The aim of this study was to quantify the effects of salinity on soil property and several indicators of soil microbial activity in existing salt affected areas of Northeast Thailand, and thereby provide information relevant to other salt affected areas with a similar alternating wet–dry tropical climate. Soils collected from nine sites showed distinct variation in soil electrical conductivity (ECe) in saturation paste extracts, ranging from 1.25 to 26.70 dS m− 1 in the wet season and from 1.80 to 28.60 dS m− 1 in the dry season. Exchangeable Na+ was the dominant cation in all soils. It increased only in the dry season, indicating that salts move up and accumulate on the soil surface during the dry season. In all sites, total soil organic C and N decreased in both seasons with increasing salinity. Cation exchange capacity (CEC) was low (less than 10 cmolc kg− 1) due to sandy texture and low organic matter of the soils. Soil microbial activities declined only in the dry season in all sites. In both seasons, there were significant negative exponential relationships between ECe and indicators of microbial activity, including microbial biomass C, the percentage of soil organic C present as microbial biomass C, microbial biomass N, the ratio of microbial biomass N to total N, and basal soil respiration. However, the metabolic quotient (qCO2) was positively correlated with ECe. These results suggest that salinity influences the soil property and microbial activity.