EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 9
Soil Survey and Soil Mapping in
Bulgaria
I. Kolchakov
S. Rousseva
B. Georgiev
D. Stoychev
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
83
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 9
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 ,
(1)
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.
84
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 (H 2O), 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<10%
of CEC. The group includes Haplic Luvisols (LVh)
and associated with them, Plano Chromic Luvisols
(LVxp), Plano Haplic Luvisols (LVhp), Eutric
Cambisols (Cme) and Eutric Planosols (Ple).
Fourth group - soils non-resistant to
acidification.
This group is characterised by pH<5.0, CEC<20
meq/100g and content of exchangeable aluminium
>10% of CEC. The group includes Dystric
Planosols (PLd), Dystric Cambisols (CMd), Humic
Cambisols (CMu), Haplic Acrisols (ACh) and
associated with them, Umbric Leptosols (LPu) and
Lithic Leptosols (LPq).
The total area of the soils with pH<7 (groups I, II
and III) occupies about 6.5 million ha, which is
about 60% of the entire territory of Bulgaria.
About two thirds of that land, 4.3 million ha, is
vulnerable (non-resistant) to acidification (pH<5).
Soil Survey and Soil Mapping in Bulgaria. Kolchakov, Rousseva, Georgiev and Stoychev
85
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 9
Figure 2: Map of the vulnerability of the soils in Bulgaria to acidification
The collected and updated soil information
facilitates an evaluation of agricultural land on the
basis of the actual and the potential suitability for
different types of land use. The digital soil maps,
including relevant soil, land evaluation and
categorisation data, are successfully used
nowadays for the purposes of land reform and
land privatisation. The soil information is used also
for land evaluation, road construction, various
agricultural, urbanisation and economic activities,
as well as to support agrarian reform and the new
cadastre of agricultural lands, for which
development is in a progress.
Eventually the GSIS will include all the data
obtained from the soil surveys at 1:25,000,
1:10,000 and 1:5,000 scales, such as soil
morphological and analytical characteristics as
well as land description, for each soil mapping
unit. This will facilitate the interpretation of all the
data needed for making technical decisions and
planning alternative variants for land use and
compiling new thematic maps. With additional
information about landscape and climatic elements,
nutrient contents and different anthropogenic
impacts, the GSIS will facilitate also predictions of
land degradation risks and planning measures for
soil conservation and land reclamation.
Outlook
The survey and collection of soil data in Bulgaria
is now well developed. Further systematisation of
all the available soil data in the GSIS will enable
their linkage with other environmental data.
86
Soil Survey and Soil Mapping in Bulgaria. Kolchakov, Rousseva, Georgiev and Stoychev
EUROPEAN SOIL BUREAU  RESEARCH REPORT NO. 9
References
Andonov, T. and Kolchakov, I. (1982). Soil map of
the region of Stara Zagora. GUGK, Sofia,
Bulgaria.
Antipov-Karataev, I.N., Galeva, V., Gerassimov,
I.P., Enikov, K., Tanov, E. and Tyurin, I. (Eds.)
(1960). The Soils in Bulgaria. Agricultural
literature Publisher, Sofia, Bulgaria.
Boyadzhiev, T. (1967). Contribution a la
connaissance des sols de la Bulgarie. These de
doctorat, Gand, Belgique.
Boyadzhiev, T. (1994a). Soil map of Bulgaria
according to the Soil Taxonomy - explanatory
notes. Soil Science, Agroochemistry and
Ecology, 29 (4-6), 43-51.
Boyadzhiev, T. (1994b). Soil map of Bulgaria
according to the FAO-UNESCO-ISRIC revised
legend. Soil Science, Agroochemistry and
Ecology, 29 (4-6), 52-56.
Boyanov, P. (Ed.). (1975). Large-scale Soil Survey
in Bulgaria, v.2. The regions of Razgrad and
Silistra. BAN, Bulgaria, 204pp.
Boyanov, P. (Ed.). (1976). Large-scale Soil Survey
in Bulgaria, v.3. The regions of Veliko Tarnovo
and Vidin. BAN, Bulgaria, 258pp.
European Soil Bureau, Scientific Committee.
(1998). The Soil Geographical Database of
Europe at scale 1:1,000,000. Version 3.28,
11/06/1998 (in progress).
Kabakchiev, I., Georgiev, B. and Bojinova, P.
(1985). Map of the land evaluation for crop
production. N. Poushkarov RISSA, Sofia,
Bulgaria.
Koinov, V. (1956). Soil Map of the Thracian
Lowlands. GUGK, Sofia, Bulgaria.
Koinov, V. and Tanov, E. (1956). Soil Map of
Bulgaria at scale 1:200,000. GUGK, Sofia,
Bulgaria.
Koinov, V. (Ed.) 1965. Large-scale Soil Survey in
Bulgaria, v.1. The regions of Kolarovgrad and
Pleven. BAN, Bulgaria, 196pp.
Koinov, V., Trashliev, H., Yolevski, M., Andonov,
T., Ninov, N., Hadzhiyanakiev, A., Angelov,
E., Boyadzhiev, T., Fotakieva, E., Krastanov,
S. and Staykov, Y. (1968). Soil map of
Bulgaria at a scale of 1:400,000. GUGK, Sofia,
Bulgaria.
Koinov, V. (Ed.) (1973a). Soil Map of Bulgaria.
In: A. Beshkov (Ed.), Atlas of Bulgaria. BAN,
GUGK, Sofia, Bulgaria.
Koinov, V. (Ed.) (1973b). Map of the Soil Texture.
In: A. Beshkov (Ed.), Atlas of Bulgaria. BAN,
GUGK, Sofia, Bulgaria.
Koinov, V. (Ed.) (1973c). Map of the Soil
Reaction. In: A. Beshkov (Ed.), Atlas of
Bulgaria. BAN, GUGK, Sofia, Bulgaria.
Koinov, V. (Ed.) (1973d). Map of the Soil
Geographical Regions. In: A. Beshkov (Ed.),
Atlas of Bulgaria. BAN, GUGK, Sofia,
Bulgaria.
Koinov, V. (Ed.) (1973e). Map of the Soil Erosion
Regions. In: A. Beshkov (Ed.), Atlas of
Bulgaria. BAN, GUGK, Sofia, Bulgaria.
Koinov, V. (Ed.) (1973f). Map of the Soil
Resources. In: A. Beshkov (Ed.), Atlas of
Bulgaria. BAN, GUGK, Sofia, Bulgaria.
Ninov, N. and Andonov, T. (1984). Soils Map of
the region of Burgas. GUGK, Sofia, Bulgaria.
Ninov, N. (1986). Map of the distribution of the
waterlogged soils in Bulgaria. N. Poushkarov
RISSA, Sofia, Bulgaria.
Stoychev D. and Kolchakov, I. (1998).
Vulnerability of main Bulgarian soils to
acidification. European Soil Bureau. Res. Rep
No 4, ISPRA, Italy.
Yolevski, M., Hadzhiyanakiev, A., Georgieva and
Kabakchiev, I. (1980). Map of the soil agroecological regions in Bulgaria at a scale of
1:600,000. KIPP Cartography, Sofia.
Soil Survey and Soil Mapping in Bulgaria. Kolchakov, Rousseva, Georgiev and Stoychev
87