Bulgarian Soils Research Articles

Сравнителна оценка на актуалната и потенциалната продуктивност на земеделски земи със слабо излужени черноземи в община Кайнарджа област Силистра

On sites with weakly leached chernozems located in the agro-ecological conditions of the municipality of Kaynardzha, Silistra region, the soil fertility and the productivity of agricultural lands were assessed in two ways: 1. Through the routinely used in Bulgaria “Methodology for work on the cadaster of agricultural lands in NRB” (Petrov et al., 1988.) and 2. Through a newly developed methodology “Modern approaches for potential assessment (Land evaluation and categorization) of agricultural lands in Bulgaria” (Radovanova, 2020). The results showed the following: In the current evaluation, the average agronomic score of the lands subject to research under non-irrigated conditions is 69, and under irrigated conditions 86, i.e. this classifies land use suitability in the 4th and 2nd categories respectively. The obtained average agronomic scores at the potential assessment of 72 and 90 under non-irrigated and irrigated conditions, respectively, classify the suitability of these lands into the 3rd category (non-irrigated) and the 1st category (irrigated). The critical comparison of the results leads to the conclusion that even for lands with some of the most fertile Bulgarian soils, the current assessment does not reveal their full production potential. For practice, both assessments should be performed simultaneously. This would most accurately orient manufacturers for the type of technological solutions and the size of the necessary investments.

Multivariate Exploratory Analysis of the Bulgarian Soil Quality Monitoring Network.

The goal of the present study is to assess the soil quality in Bulgaria using (i) an appropriate set of soil quality indicators, namely primary nutrients (C, N, P), acidity (pH), physical clay content and potentially toxic elements (PTEs: Cu, Zn, Cd, Pb, Ni, Cr, As, Hg) and (ii) respective data mining and modeling using chemometrical and geostatistical methods. It has been shown that five latent factors are responsible for the explanation of nearly 70% of the total variance of the data set available (principal components analysis) and each factor is identified in terms of its contribution to the formation of the overall soil quality-the mountain soil factor, the geogenic factor, the ore deposit factor, the low nutrition factor, and the mercury-specific factor. The obtained soil quality patterns were additionally confirmed via hierarchical cluster analysis. The spatial distribution of the patterns throughout the whole Bulgarian territory was visualized via the mapping of the factor scores for all identified latent factors. The mapping of identified soil quality patterns was used to outline regions where additional measures for the monitoring of the phytoavailability of PTEs were required. The suggested regions are located near to thermoelectric power plants and mining and metal production facilities and are characterized by intensive agricultural activity.

Bacillus Strains as an Effective Treatment of Mobile Forms of Phosphorus in Bulgarian Soils

Strains of genus Bacillus have the potential to increase the availability of phosphorus to plants by the dissolution of inorganic phosphate, which favours the growth of plant species and that has an important economic and agricultural impact. Soils with low phosphate intensity (Lеаched chernozem) were enriched with poorly soluble phosphorus compounds and inoculated with the tested newly isolated strains from genus Bacillus (Bacillus subtilis T 2, Bacillus amyloliquefaciens T 3, Bacillus subtilis T 4, Bacillus subtilis T 10, Bacillus thuringiensis T 17 and Bacillus cereus Т 18). Six newly isolated strains from different regions in Bulgaria were identified by classical phenotypic techniques and 16S rDNA sequence analysis. Tested strains were inoculated (2 ml and 15 ml) in the soil and incubated for 25 days at 28oC. After the incubation period, the degradation of phosphorite flour to available phosphorus was examined by the classical method of Egner-Riehm and by extraction with CaCl2. A vegetation experiment was conducted with a test plant Pelargonium zonale, characterized by its ability to absorb large amounts of phosphorus. A peat substrate enriched with all macro-and microelements was used, and phosphorus was added to the medium in the form of phosphorite flour. The amounts of phosphorus absorbed by one plant Pelargonium zonale treated with newly isolated strains Bacillus subtilis T 10 and Bacillus cereus T 18 absorbed 23% more phosphorus than the control variant. As a result of the experiments, it was found that the studied strains have a positive impact on the increase of phosphorus mobility in soils with low phosphate intensity treated with hardly degradable phosphors.

Study on pH in water and potassium chloride for Bulgarian soils

Soil pH is commonly measured in water pH(H 2 O) or pH(KCl). The relationship between pH(H 2 O) and pH(KCl) across all Bulgarian soils were investigated and results examining the effect of soil type on the relationship were presented. Several functions were used to estimate dependence between the two measures. For all soils and depths, a linear regression accounted for 95.32% of the variation, which predicts pH(KCl) very well. From the analysis of data follows that they were differentiated into three clusters.

Establishment of geochemical background and threshold values for 8 potential toxic elements in the Bulgarian soil quality monitoring network

Establishment of geochemical background and threshold values of potentially toxic elements is essential for soil management activities. Available topsoil data collected in the Bulgarian soil quality monitoring network are explored for the concentrations of the potentially toxic elements (PTEs) of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. The ‘median + 2MAD’ and TIF methods for obtaining geochemical threshold values, which differentiate sampling sites with background from those with unusually high element concentrations, are presented. Comparison of the derived national geochemical threshold values with those obtained in European studies outlines the specificity of the Bulgarian PTE background concentrations among the other southern European countries. The threshold values for Cd, Cu, Ni, Pb and Zn are more similar to those derived from the northern European countries since the As and Cr ones are more close to the values derived for southern Europe. The geochemical threshold of Hg is almost one order of magnitude as high as the southern European derived value. The usage of geochemical threshold values for soil risk assessment is suggested by comparison with soil quality guideline values adopted in other countries. The combination of threshold values based on 90th percentile with geochemical mapping identifies the priority areas for further assessment. Regions with more than 2 PTEs (2.26% of the Bulgarian territory) are suggested for detailed (eco)toxicological assessment.

PAHs in fly ash from lignite combustion

This paper describes state-of the art for isolation and determination of polycyclic aromatic hydrocarbons (PAHs) in fly ash from lignite combustion in Maritza East Thermal Power Plant, Bulgaria. Total sum of-17 microg/kg solid by-product PAHs was determined. The profile of PAHs distribution according to the number of aromatic rings in the molecule (R) was determined. Organic extracts were mainly composed by PAHs, their alkylated homologues and heteroatom containing counterparts with dominance of three/four cyclic aromatic compounds. Respectively, relative carcinogenic potency values for PAHs compared to Benzofajpyrene with TEFEPA =1 was not high - 0,07385. Seventeen PAHs, some of them in the list of USEPA for priority pollutants with expressed carcinogenic/mutagenic potential, were identified and quantified by mass spectroscopy (GC/MS/MS) and d-PAHs as internal standards. Determined values for contents of PAHs under regulation were lower than their backgrounds in Bulgarian soils. Nevertheless PAHs in combustion fly ash should be monitored because of high solid by-products annual production and problems of reuse

Content and Behavior of Radiocesium in Undisturbed Bulgarian Soils

Content and Behavior of Radiocesium in Undisturbed Bulgarian Soils

Arsenic in gulls: A global overview

The content and availability of Pb, Cu and Zn were determined by the methods of soil extractions with aqua regia, 1 M NH4NO3 and 1 M NH4Ac. Reclaimed soils, which differ in land use, the duration of post reclamation development, geological and geographical characteristics were included in the study. In most pedons trace element total contents are irregular along depth and close to the background values in Bulgarian soils (Pb — 26 μg/g, Cu — 34 μg/g and Zn — 88 μg/g). The copper content greatly varies between the minimum of 8.5 μg/g and the maximum of 500 μg/g. The latter is defined as an intervention concentration by the Bulgarian legislation, and is accepted as a toxic threshold which affects soil functions, the environment and human health.Mobile concentrations of Pb, Cu and Zn are non-toxic assuming 8 μg/g for Cu, 4 μg/g for Pb and 43 μg/g for Zn as acceptable limits of available heavy metals in Technosols with slightly alkaline pH (7.0 - 8.0). The acidic pH (< 6.0) increases the solubility and desorption of zinc and copper, but diversely influences the bioavailability of lead. In acidic Technosols Pb and Cu mobile contents could exceed the Prüeß critical level of 1 μg/g and may provoke independent and joint toxic effects. The lithogenic origin of Cu toxicity which amounted to 47.7 μg available Cu/g soil shows the most serious risk of environmental pollution.Intensive weathering of soil surface layers does not accelerate the trace element bioavailability. Pb, Cu and Zn mobility mostly depends on pH, the content and mineralogy of fine earth fractions (< 0.01 mm) and organic carbon pools in studied soils.

Pb, Cu and Zn geochemistry in reclaimed soils (Technosols) of Bulgaria

The content and availability of Pb, Cu and Zn were determined by the methods of soil extractions with aqua regia, 1M NH4NO3 and 1M NH4Ac. Reclaimed soils, which differ in land use, the duration of post reclamation development, geological and geographical characteristics were included in the study. In most pedons trace element total contents are irregular along depth and close to the background values in Bulgarian soils (Pb — 26μg/g, Cu — 34μg/g and Zn — 88μg/g). The copper content greatly varies between the minimum of 8.5μg/g and the maximum of 500μg/g. The latter is defined as an intervention concentration by the Bulgarian legislation, and is accepted as a toxic threshold which affects soil functions, the environment and human health.Mobile concentrations of Pb, Cu and Zn are non-toxic assuming 8μg/g for Cu, 4μg/g for Pb and 43μg/g for Zn as acceptable limits of available heavy metals in Technosols with slightly alkaline pH (7.0 - 8.0). The acidic pH (<6.0) increases the solubility and desorption of zinc and copper, but diversely influences the bioavailability of lead. In acidic Technosols Pb and Cu mobile contents could exceed the Prüeß critical level of 1μg/g and may provoke independent and joint toxic effects. The lithogenic origin of Cu toxicity which amounted to 47.7μg available Cu/g soil shows the most serious risk of environmental pollution.Intensive weathering of soil surface layers does not accelerate the trace element bioavailability. Pb, Cu and Zn mobility mostly depends on pH, the content and mineralogy of fine earth fractions (<0.01mm) and organic carbon pools in studied soils.

Technogenic radionuclides in undisturbed Bulgarian soils

This work presents data for the activity concentration of artificial radionuclides in soils from different regions in Bulgaria for the period 1985–2011. The subjects of the study were undisturbed soils from mountainous, hilly, and plain areas. Special attention has been paid to the contamination with the long-lived technogenic radionuclides cesium-137, strontium-90, plutonium-238, and plutonium-239+240. 137Cs was measured by low level gamma spectrometry and 90Sr by radiochemical separation and low level beta counting. The isotopes of plutonium were measured by alpha-spectrometry after a radiochemical procedure of purification and concentration.Cesium-137 and strontium-90 were the main technogenic radionuclides detected in the examined Bulgarian soils few years after the Chernobyl NPP accident. Their content in the soils from high mountain areas is several times higher than that in the soils from the plane areas in the northern part of the country. High heterogeneity in the pollution has been observed. Mean soil activity concentration levels of up to 250Bqkg−1 for 137Cs and 14Bqkg−1 for 90Sr were found in different years. The maximal values registered in separate soil samples were about 1300Bqkg−1 (137Cs) and 24Bqkg−1 (90Sr). The activity concentration levels for 239+240Pu varied between 0.1 and 3.7Bqkg−1. The results indicate that the radioactive pollution of the Bulgarian soils with artificial radionuclides is a result of global fallout and Chernobyl nuclear power plant accident.

A novel cyclodextrin glucanotransferase from alkaliphilic Bacillus pseudalcaliphilus 20RF: Purification and properties

A new cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from the obligated alkaliphile Bacillus pseudalcaliphilus 20RF, isolated from Bulgarian soils, was purified up to 18-fold by ultrafiltration and starch adsorption with a recovery of 63% activity. The enzyme was a monomer with a molecular weight 70 kDa estimated by SDS-PAGE. The CGTase exhibited two pH optima at pH 6.0 and 9.0 and was optimally active at 60 °C. The enzyme could be effectively used for conversion of raw starch into cyclodextrins (CDs) in a wide pH range, from 5.0 to 10.0 and temperatures 60–70 °C. The enzyme was more heat resistant after its pretreatment in alkaline pH 9.0 at high temperatures 65–70 °C, than at pH 6.0 under the same reaction conditions. The CGTase showed a significant stability in the presence of 15 mM various metal ions and reagents after 30 min incubation at 25 °C. The purified CGTase could be used for an efficient cyclodextrin production without any additives which is of an industrial interest. The achieved high conversion of an insoluble raw commercial corn starch into cyclodextrins (47%) with production of only two types of cyclodextrins, β- and γ-CD (80%:20%) in alkaline pH 9.0, makes B. pseudalcaliphilus 20RF CGTase industrially desired for cyclodextrin manufacture.

Determination of activity ratios of 238,239+240,241Pu, 241Am, 134,137Cs, and 90Sr in Bulgarian soils

The origins of different artificial radionuclides found in soils from Northern and Southern Bulgaria was determined by measurements of their actual concentrations and respective ratios. On the basis of the measured mobility and concentrations of the investigated radionuclides in soils, it was estimated that after the Chernobyl accident the mean depositions of fresh 137Cs were 3.0 ± 2.5 kBq/m2 for Northern Bulgaria and 15 ± 7 kBq/m2 for Southern Bulgaria. As a result of global fallout following atmospheric nuclear weapon tests in the 1950s, mean depositions (corrected to 1965) were calculated for Northern and Southern Bulgaria as follows: for 90Sr—1.0 ± 0.5 and 2.3 ± 1.3 kBq/m2, 238Pu—1.3 ± 0.8 and 2.8 ± 1.6 Bq/m2, 239+240Pu—15 ± 14 and 47 ± 38 Bq/m2, and 241Pu—520 ± 200 and 760 ± 260 Bq/m2.

DYNAMICS OF THE RADIOACTIVE POLLUTION IN THE SURFACE LAYER OF SOILS IN BULGARIA TWENTY YEARS AFTER THE CHERNOBYL NUCLEAR POWER PLANT ACCIDENT

The twenty years period past after the contamination with radionuclides in 1986, as a result of the accident in the Chernobyl’s NPP, allowed the accumulation of rich data base for the radiation status of the soils in Bulgaria. Objective of many years studies were virgin soils from high mountain areas, hilly and flat (the region of Kozlodouy NPP and the Danube river valley). Ceasium-137 and strontium-90 were the main men-made radionuclides detected in the examined Bulgarian soils, few years after the accident. The content of ceasium-137 and strontium-90 in the soils from high mountain areas (Rodopa and Rila mountains) is several times higher then that in the soils from Northern Bulgaria and Sofia field. High non-homogeneity in the pollution within small areas (scores of square meters even) was determined. No significant horizontal redistribution was observed for the period after 1986. The tendency of changes in the radioactive status of the soils in Bulgaria after the accident at the Chernobyl Nuclear Power Plant is not due to trans-border transfer of radioactive materials or to any breakdown at the Kosloduy Nuclear Power Plant.

Novel thermostable serine collagenase from Thermoactinomyces sp. 21E: purification and some properties

A thermophilic actinomycete strain Thermoactinomyces sp. 21E producing a highly thermostable serine collagenase was isolated from Bulgarian soil. The collagenase, produced extracellular by Thermoactinomyces sp. 21E, was purified to homogeneity by heat treatment, ultrafiltration, saturation with ammonium sulfate and gel filtration chromatography with a 101-fold increase in specific activity and 58% recovery. The collagenase has a relative molecular mass of 50000 by SDS-PAGE. The optimum temperature for the enzyme activity was 60-65 degrees C in the absence of Ca(2+) and 70-75 degrees C in the presence of Ca(2+). About 40% of the original activity remaining after incubation at 85 degrees C for 30 min in the presence of Ca(2+). The optimum pH for the enzyme activity was 9.0-9.5 and the enzyme was stable for 1h at 70 degrees C in the pH range from 7.5 to 12.5. The collagenase was strongly inhibited by active-site inhibitors of serine protease PMSF and DFP, which indicated that the enzyme is serine protease. The enzyme activity was completely inhibited by Hg(2+), Cu(2+) and Fe(2+). However, Ca(2+ )strongly activated the collagenase activity. The collagenase from Thermoactinomyces sp. 21E showed high activity toward type I collagen, acid-soluble collagen, gelatin and Pz-PLGPR. However, elastin for collagenase was inert as substrate. The properties of the collagenase from strain 21E suggest that this enzyme is a new collagenolytic protease that differs from the collagenases and serine proteases reported so far.

Simulation of water flow and nitrogen transport for a Bulgarian experimental plot using SWAP and ANIMO models

Unsaturated zone models are useful tools in predicting effects of measures and can be used to optimise agricultural practice aiming to minimise the impact on the environment. However, current soil models have a varying degree of abstraction level referring to simulated processes in time and space. In the framework of an EU funded project the SWAP (Soil–Water–Atmosphere–Plant) and ANIMO (Agricultural-Nutrient-Model) models were tested for an experimental arable plot in Bulgaria. SWAP was used to simulate water flow in the soil while ANIMO describes nitrogen movement and transformations. The objectives of this study are: (i) to show results of the combined application of water and nitrogen dynamics of originally Dutch models SWAP and ANIMO for specific Bulgarian soil and hydrological conditions; (ii) to calibrate and evaluate SWAP and ANIMO models by comparing numerical results with field measurements collected for an arable field in western Bulgaria and (iii) to analyse possible contamination of groundwater due to agricultural practice in the considered region. Further a short description of the experimental plot, as well as information about parameters of the investigated soil profiles, is provided. The obtained SWAP results evidenced that the model gives sufficient adaptation for soil water dynamics. The simulations of ANIMO for nitrogen cycle show greater divergence with observations but are satisfactory precise for the purposes of assessing land use impact on groundwater quality. In general, differences between model results and field measurements do not exceed 10–15%. For the experimental plot predictions indicate nitrate-N concentrations less then 5 mg/l in deeper soil compartments and low downward annual flux containing 0.133 kg N/ha. These results indicate that there is no serious pollution of the shallow groundwater table by nitrogen resulting from land use and agricultural activities.

New index to remove from a spectral mixture an unknown spectral component

More than one spectral classes are usually found within a pixel when measuring the spectral reflectance (the spectral reflectance coefficients (SRC) in particular) of natural formations in the visible (VIS) and near infrared (NIR) spectral ranges. The spectral mixture “soil-vegetation” is a typical example. The decomposition of this mixture is strongly impeded because only the mixture SRC are usually available, the soil SRC and the vegetation coverage coefficient p not being known in advance. This is especially true for remotely sensed data in field experiments. Under the assumption that the soil SRC are a linear function of the wavelength two SRC transforms were defined and studied in previous papers of the authors. The second transform is the θ coefficient, which is free of the unknown linear soil component as well as of the unknown coverage coefficient p. In previous studies of the authors θ was examined in the case when the soil SRC may be approximated by one straight line. In this work, θ was obtained and studied for soil types that may be satisfactory piece-wise approximated by two different crossing straight lines within the VIS and NIR ranges. Thus, the θ coefficient may be employed to eliminate the unknown soil SRC from the measured mixture SRC in the case when the soil SRC are nonlinear wavelength function which may be fitted by two straight lines. Examples of USA and Bulgarian soil types are given in the study, which meet this requirement.

Characterization of the enzyme complexes produced by two newly isolated thermophylic actinomycete strains during growth on collagen-rich materials

The collagenolytic enzyme complexes secreted by two thermophilic Actinomycetes newly isolated from Bulgarian soils were characterized for their possible application for treating collagen-rich materials. The strains were identified as belonging to genera Microbispora and Thermoactinomyces. The molecular masses of the enzymically active fractions determined by gel chromatography on Sephadex G-100 showed values between 46 and 140 kDa. The enzyme complexes produced by both strains were stable against temperature changes and high ethanol concentrations, which allows effective elimination of different by-products (pigments, nutrient medium components, and metabolites). The comparison with clostridiopeptidase A as well as the inhibitory analysis showed that these enzymes might be considered as “collagenase-like” enzymes. Preliminary experiments showed that a mixture of both enzyme preparations could be applied for pre-treatment of collagen-rich raw materials, e.g., in the pelt industry.

Influence of clinoptilolite and compost on soil properties

Compost from municipal sewage sludge, bark plus zeolite, and zeolite alone were used in this study to evaluate their influence on soil properties and humus characteristics. Two incubation experiments were conducted in two low humus content soils from Bulgaria (Typic Xerochrept) and Greece (Typic Rhodoxeralf). Soil alone, soil with zeolite, and soil with compost in various rates were incubated for 90 days (24±1°C, moisture content about 60% of field capacity). The experimental design was randomized complete blocks with four treatments each replicated four times. At the end of incubation experiment samples were taken, and the basic chemical properties as well as humus composition were determined. The pH, electrical conductivity and NO3-N concentration were determined in samples taken every 15 days. The results showed that zeolite increased soil pH and exchangeable potassium (K). Compost increased available phosphorus (P) in the low P Bulgarian soil and electrical conductivity. A strong positive relationship between electrical conductivity and NO3-N was recorded. Soil pH was negatively correlated with NO3-N concentration for Bulgarian soil. Composted sewage sludge also significantly increased soil organic matter content and led to formation of condensed humic acids.

Isolation and distribution ofStreptomyces populations with heat-resistant collagenolytic activity from two protein-rich areas in Bulgarian soils

Two sites in Northeastern of Bulgaria were investigated as a source ofStreptomyces populations to screen for production of heat-resistant collagenase. The distribution and diversity of collagenolytic activity inStreptomyces populations from protein-rich residue were studied. Collagenolytic activity was found in 14% of the 350 tested strains. Poor collagenase producers generally dominated (70%). Highly active collagenase producers were rarely found (12%) and they were mainly fromAlbus andRoseus groups. The isolatedStreptomyces cultures developed a constitutive collagenase activity. Two promising, highly active, producers of heat-resistant collagenase were selected and identified asStreptomyces candidus 91 andS. cremeus 3. The investigatedStreptomyces collagenases were active over a broad range of temperature (40–80°C) and a narrow range of pH values (6.5–8.5), with optima at 40°C and pH 7.5.

Derivation of soil water capacity parameters from standard soil texture information for Bulgarian soils

Prediction of total porosity and volumetric water content at field capacity, and permanent wilting point have been evaluated for their possible applicability to supply important missing soil information. The results were compared to the experimental data from Bulgaria. Also the possibility is explored to convert soil particle size distribution data as determined according to the soil standards in Bulgaria to the following particle size fractions (‘sand’ (0.05–2.0 mm in diameter), ‘silt’ (0.002–0.05 mm) and ‘clay’ (smaller than 0.002 mm)). The approach tested for calculating total porosity and volumetric water content at field capacity, and permanent wilting point yielded values in close agreement with the measured ones.