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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).

Soil erosion is a serious environmental problem and a threat to the sustainable agriculture production. Little information is available on enzyme activities of eroded soils in Bulgaria, especially on their relations to the degree of erosion and soil properties. In this work, slightly, moderately and severely eroded Chromic Luvisols under different land use (pasture, crop field and virgin) were studied. Enzyme activities (invertase, catalase and phosphatase), total nitrogen, total carbon, available phosphorus contents and soil particle distribution were determined and possible relations between them were examined. Data showed that enzyme activities tended to lower with increasing the degree of erosion. This was better pronounced for invertase and phosphatase in pasture and virgin soils. Depending on land use, all enzyme activities decreased in the order pasture > virgin > crop field soils, showing positive impact of soil cover and negative effect of cultivation practices. Soil invertase and phosphatase activities were in close relations with soil carbon content. The activities of catalase and phosphatase correlated positively with soil clay. Invertase only was in positive relation with soil silt and in negative relation with the sand content. Data obtained are intended to contribute to development of biological indicators of eroded soils.

The study was performed to evaluate the nutritional value and antioxidant properties of cowpea grain, where plants were grown under conditions of tripartite symbiosis (cowpea plants, nitrogen-fixing bacteria (Bradyrhizobium japonicum) and arbuscular mycorrhizal fungi, (Glomus intraradices) without fertilization. Cowpea plants (Vigna unguiculata (L.) Walp) cv. Hrisi were grown in a glasshouse until the full maturity of grain on the Alluvial meadow soil (Eutric Fluvisol) at three levels of water-holding capacity (40, 60 and 80%). Bradyrhizobium japonicum solely and in combination with arbuscular mycorrhizal fungi increased the content of proteins, soluble sugars and total phenols in the cowpea seeds. When dual inoculation has applied the levels of proteins and soluble sugars in the cowpea grain did not reduce at 40%, nor at 80% in comparison with the optimal water-holding capacity level (60%). Antioxidant capacity at 40% water-holding capacity was determined by the increased content of water soluble antioxidants, flavonoid content and increased ferric reducing power activity and increased antioxidant levels was expressed more distinguished in the treatments with dual inoculation. Slight change of antioxidants in the grain of cowpea was established at an elevated level of water supply. Nutritional value of a grain of cowpea after dual inoculation with Bradyrhizobium strains and Glomus intraradices was not determined by the water-holding capacity levels.