Microbiological Parameters of Technosols Monitored for Hydrophobicity

Soil hydrophobicity causes reduced water infiltration rate and has a negative impact on plant growth. Reports on hydrophobicity of Technosols are limited, and in Bulgaria studies have been initiated only recently. The present work aimed to monitor two Technosols (non-vegetated and afforested with Pinus nigra) located near Obruchishte (Maritsa-Iztok coal mines) for hydrophobicity level and to assess their microbiological status. In total, 24 soil samples from 12 sampling points and two soil depths (0-10 сm and 10-20 сm) were analyzed for hydrophobicity, moisture content, numbers of cultivable microorganisms, basal respiration and microbial biomass carbon. The hydrophobicity was measured by water-drop-penetration-time (WDPT) test. Microbial numbers were determined by plate counts technique. Sample incubation in closed vials was used to determine basal respiration and microbial biomass carbon. Among the studied samples, 42% possessed severe hydrophobicity, 37% were strongly hydrophobic and 21% were non-hydrophobic (hydrophilic). Both soils were characterized with low numbers of bacteria, actinomycetes and fungi (102 CFU/g), and low levels of basal respiration rate (0.13-6.54 mg CO2-C/100g/24h) and microbial biomass carbon (1.57-18.86 mg C/100g). Values widely differed among sampling points and layer depths because of the high heterogeneity of the soil substratum. The hydrophobic samples contained a relatively higher amount of saprotrophic fungi than hydrophilic ones..