Soil Survey and Soil Mapping in Bulgaria

EUROPEAN SOIL BUREAU ⎯ RESEARCH REPORT NO. 9 Soil Survey and Soil Mapping in Bulgaria I. Kolchakov S. Rousseva B. Georgiev D. Stoychevh Institute of ...
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Soil Survey and Soil Mapping in Bulgaria I. Kolchakov S. Rousseva B. Georgiev D. Stoychevh Institute of Soil Science ‘N. Poushkarov’, 7 Shosse Bankya Street, 1080 Sofia, Bulgaria

Introduction The structure of the soil cover of Bulgaria is a result of the evolution of natural processes from the Pliocene to the present day Sub Atlantic, including neotectonic and anthropogenic influences. The structure of the soil cover is additionally complicated by the variability of modern climate conditions. Five types of pedoclimate regimes can be distinguished in the country: cryo-udic, meso-udic, meso-ustic, mesoxeric and thermo-xeric (Boyadzhiev, 1967). As a result, 20 out of a total of 28 FAO soil map units can be found on the relatively small territory of Bulgaria (Boyadzhiev, 1994b). For the last 90 years, collecting, preserving, updating and using soil information have been the main aim of investigations involving soil survey, diagnostics, classification and mapping.

Soil Mapping The organised systematic study of Bulgarian soils, commissioned by the Ministry of Agriculture, started under the guidance of Nikola Poushkarov in 1911. In 1913 Poushkarov presented the first soil map of the region of Sofia at a scale of 1:126,000. The first soil map of Bulgaria was prepared at a scale of 1:500,000 in 1931. This map showed the geographic distribution of the main soil units. The soil map of Bulgaria at a scale of 1:200,000, prepared by Koinov and Tanov (1956), identified a significantly larger number of soil units, compared to those identified in the map of 1931. The monograph ‘Soils of Bulgaria’ (AntipovKarataev et al., 1960) collected all the available data on morphological, physical, chemical and physico-chemical characteristics of the main soil units. Systematic large-scale soil survey started in 1956.

A soil map of Bulgaria at a scale of 1:400,000 was published in 1968 (Koinov et al., 1968). This map was based on the information obtained from the soil survey at a scale of 1:25,000 of over 65% of the country’s territory. The map identified 67 soil units at group and subgroup level, soil texture class and degree of erosion. Figure 1 shows a reduced version of the digitised soil map of Bulgaria at 1:400,000 scale. After generalisation of the map at 1:400,000 scale, a soil map at a scale of 1:1,000,000 was compiled and published in the geographic atlas of Bulgaria (Koinov, 1973a). It distinguished 45 soil units. The geographic atlas of Bulgaria included also maps of the geographical distribution of the soils according to their texture (Koinov, 1973b) and soil reaction (Koinov, 1973c), both at 1:3,000,000 scales; maps at 1:2,000,000 scales of the soil geographical (Koinov, 1973d) and soil erosion regions (Koinov, 1974e); and the distribution of the soil resources within the administrative districts of the country (Koinov, 1973f). Soil survey at a scale of 1:10,000 started in 1971. By 1988 the soils of Bulgaria had been mapped at 1:25,000 scale and the soil survey at a scale of 1:10,000 was in a progress. Currently, soil maps at a scale of 1:10,000 cover almost the entire territory of Bulgaria. In addition, soil survey and maps at scales from 1:5,000 to 1:1,000 cover land with particular problems, such as salinisation and pollution with heavy metals, arsenic, oil products or radionuclides. In 1994, the soil map of Bulgaria at a scale of 1:1,000,000 was completed based on the 1990 FAO revised legend. This map was prepared for incorporation in the soil geographical database of Europe at 1:1,000,000 scale (European Soil Bureau, 1998).

Soil Survey and Soil Mapping in Bulgaria. Kolchakov, Rousseva, Georgiev and Stoychev



Soil information, databases and monitoring According to the extended systematic list of the soils in Bulgaria, 200 soil units have been defined, each of them carrying coded information about profile depth, degree of erosion, classes of soil texture and stoniness, parent material, slope and land evaluation. The formula for coding the soil units is expressed as: Na

L1,2,3,... N1,2,3,...

Nb ,


where: Na is the land category, according to the Bulgarian land evaluation system; L 1,2,3,… are codes for soil description; Nb is the field index and N 1,2,3,… are the codes for texture classes, stoniness, parent materials, etc. The defined soil units are characterised by profile morphological description, particle-size distribution, pH and the amounts of total carbon, nitrogen, phosphorus and calcium carbonates, based on the data from 50,000 main soil profiles. In addition, the information for more

than 250 soil profiles, representing the main soil varieties, is expanded by analytical data on the humus content, hydrological properties, chemical composition, Fe and Al status, CEC, base saturation, etc. Archives maintained at administrative level have been created from the basic documents such as soil survey records, remote sensing information, laboratory data forms, climatic parameters, etc. All the relevant information is kept in special Soil Survey Books in the form of text, tables and maps. The enormously important information about the soil resources is now summarised and systematised by the National Soil Survey Service creating a Geographic Soil Information System (GSIS). Digitisation of the existing soil maps to the lowest taxonomic levels was an important step in building up the GSIS. All paper and electronic records are deposited at the Research Institute of Soil Science and Agroecology, the National Centre for Agrarian Sciences, the Ministry of Agriculture and other government institutions.

Figure 1: Generalised version of the digitised soil map of Bulgaria at 1:400,000 scale.


Soil Survey and Soil Mapping in Bulgaria. Kolchakov, Rousseva, Georgiev and Stoychev

EUROPEAN SOIL BUREAU ⎯ RESEARCH REPORT NO. 9 In addition to the soil survey, soil agrochemical survey and maps at a scale of 1:25,000 cover the arable land in Bulgaria. The records from the agrochemical soil survey include information about the total and available forms of the macroand microelements and data of the main soil physical and chemical characteristics. The relevant information is updated periodically. Monitoring of the soil resources in Bulgaria has been in a progress for some time. It is based on 146 SOTER units, selected in accordance with the digital soil and geological maps of the country. The soil monitoring aims at maintaining actual information about the soil vulnerability to different degradation processes, such as erosion, salinisation, acidification, water logging, heavy metal pollution and groundwater pollution. Monitoring points have been selected for collecting records of the background values and their modification due to different anthropogenic impacts.

Applications Since 1956 the data from the large-scale soil survey have been used to compile soil maps of Bulgarian geographical regions at 1:50,000 scale (Koinov, 1956) and administrative districts at 1:100,000 scale (Koinov, 1965; Boyanov, 1975, 1976; Andonov and Kolchakov, 1982; Ninov and Andonov, 1984). Thematic maps of the whole of Bulgaria have been prepared also to facilitate the soil agro-ecological partition at a scale of 1:600,000 (Yolevski et al., 1980), land evaluation for crop production at 1:1,000,000 scale (Kabakchiev et al., 1985) and the distribution of waterlogged soils at 1:400,000 scale (Ninov, 1986). Soil maps of some main catchments have been compiled for the purposes of diverse national and international research projects. Boyadzhiev compiled soil maps of Bulgaria at a scale of 1:3,000,000 according to the Soil Taxonomy (Boyadzhiev, 1994a) and the revised legend of FAO-UNESCO-ISRIC (Boyadzhiev, 1994b). An example of a thematic soil map is presented in Figure 2. The map of soil vulnerability to acidification was prepared by Stoychev and Kolchakov (1998), based on the soil survey records and the soil map of Bulgaria at a scale of 1:1,000,000. The main soil units are grouped according to their vulnerability to acidification on the basis of the data for pH (H2O), cation exchange capacity (CEC), base saturation (BS), exchangeable acidity and clay content in the top

layers of virgin and arable lands. The relevant soil survey data and the expert evaluations have shown that the soils could be classified in four broad groups:

First group - soils resistant to acidification This group is characterised by pH>7.5, CEC>35 meq/100g, BS=100% and high content of carbonates from the top of the soil profile. The group includes Haplic Kastanozems (KSh), Rendzic Leptosols (LPr), Calcaric Fluvisols (FLc), Haplic Solonetz (SNh), Gleyic Solonchaks (SCg) and associated with them Calcaric Regosols (RGc), Lithic Leptosols (LPq) and Calcaric Phaeozems (PHc).

Second group - soils moderately resistant to acidification. The main parameters of this group range as follows: pH 6.0-7.5, CEC 35-60 meq/100g, BS 8595%, clay content >40% and domination of 2:1 clay minerals. The group includes Haplic Chernozems (CHh), Eutric Vertisols (VRe), Luvic Phaeozems (Phi), Chromic Luvisols (LVx) and the associated with them Eutric Regosols (Rge), Vertic-Chromic Luvisols (Lvxe) and Eutric Fluvisols (Fle).

Third group - soils poorly resistant to acidification. The main parameters of this group range as follows: pH 4.8-6.0, CEC 25-35 meq/100g, BS 5085% and content of exchangeable aluminium