Relationships Between Microbial Parameters and Soil Properties in a Hydrophobic Spolic Technosol

Data on microbiology of water repellent (hydrophobic) soils in Bulgaria are scarce. This work aimed to find out relations between microbiological indicators, hydrophobicity level and other soil properties in a Spolic Technosol. Samples from 0-10 cm and 10-20 cm soil depth of a fly ash reclaimed soil covered with tuft vegetation and located near Obruchiste area were collected. Main microbiological (basal respiration - BR, microbial biomass carbon content -Cmic, amount of main microbial groups –CFU), chemical (organic carbon, available N, P and K contents) and physical (hydrophobicity level, moisture, sand and clay contents) properties were determined. It was found that the Technosol was hydrophobic in most of the monitoring points. Half of the samples were severely or extremely hydrophobic (assessed by water-drop-penetration time) and the hydrophobicity level was higher in the subsurface layer. The Spolic Techosol under tuft vegetation was characterized with low numbers of heterotrophic bacteria, actinomycetes and oligotrophic microorganisms (1-40 x 102 CFU/g) at 0-20 cm depth. As a whole, low BR rate (0.51-5.43 mg CO2/g/ 24h) and low Cmic values (2.37-18.18 mg C/100g) were established for both layers. Weak relationships of microbial parameters with organic carbon, humic acid, fulvic acid and clay contents were noticed in this soil. Significant correlations of the amount of fungi and actinomycetes with available nutrient and moisture contents were found. In general, a trend of positive relationships of fungi, actinomycetes and cellulolytic microorganisms with soil hydrophobicity was established. The relative parts of fungi and actinomycetes increased in the hydrophobic samples comparing to non-hydrophobic ones. Microbial biomass carbon tended to increase with increasing the hydrophobicity level. Data pointed on close positive relationships of microbial parameters studied with the hydrophobicity in this Technosol. Our results add new information to the monitoring study of hydrophobic Technosols from Maritsa-Iztok coal-mining region (Bulgaria).