International Symposium on Black Soils (ISBS18): Protect Black Soils, Invest in the Future, 10 - 12 September 2018, Harbin, China

1. Status of Black soil resources in Bulgaria:
Chernozems and Smolnitsa soil types
Shishkov Toma
Institute of soil science, agrotechnology and plant protection “Nikola Poushkarov”

2. Black Soils distribution (Chernozem and Smolnitsa soil varieties) on the territory
of Bulgaria according to Soil Map 1: 400 000

3. Black Soil units (Chernozems and Smolnitsa) and area of cover
according to Soil Map 1:400 000
Calcareous chernozems, loamy
Eroded calcareous and typical chernozems
Eroded leached chernozems
Heavy chernozems and karasoulouk clayey
Leached chernozems, heavy loamy
Meadow chernozems, moderately to heavy loamy
Podzolized (lessive) chernozems and dark grey forest soils, heavy loamy
Slightly leached chernozems, loamy
Strongly leached chernozems, heavy loamy
Typical chernozems, loamy
Leached smolnitza, clayey
Calcareous and typical smolnitza slightly clayey
Meadow smolnitza, slightly clayey
Eroded leached smolnitza
Soil units according to Soil Map 1:400 000 Area, (ha)
Calcareous chernozems, loamy and heavy loamy 448 056,2
Typical chernozems, loamy 171 081,0
Slightly leached chernozems, loamy 132 878,5
Leached chernozems, heavy loamy 724 816,1
Strongly leached chernozems, heavy loamy 77 747,9
Heavy chernozems and karasoulouk, clayey 59 402,8
Podzolized (lessive) chernozems and dark grey forest soils, heavy
loamy
202 419,3
Meadow chernozems, moderately to heavy loamy 138 495,5
Eroded calcareous and typical chernozems 204 532,1
Eroded leached chernozems 170 646,6
Total area of Chernozem soil varieties 2 330 076,3
Calcareous and typical smolnitza, slightly clayey 40 167,6
Leached smolnitza, clayey 458 100,7
Meadow smolnitza, slightly clayey 17 579,2
Eroded leached smolnitza 60 460,6
Total area of Smolnitsa soil varieties 576 308,2

4. Bulgarian proposal for definition of Black Soils:
1. Group of chernozems – etalon for soil’s potential productivity
result of balanced accumulation of humic organic substances and
development of remarkable structure in a harmony with processes
of natural ambient environment
2. Group of Smolnitsa – intense black soils of potential
productivity, with high proportion of smectitic clay and vertic
properties

5. In the group of Black Soils
compare to the Chernozems the main difference of Smolnitsa soil units is:
1. Clay mineralogy is dominated by stable minerals of smectites group. This fact
implies particularly shrinking and swelling activity and produce the cracks
2. Initiate self-pedoturbation, the annual repetition of this cycle produces the
uniform soil profile
3. Little fluctuation of soil solutions within the smolnitsa profile
4. Content of organic matter is low and change in organic matter content does
not result in change of soil color
5. Unfavorable physical properties
6. The internal porosity of aggregates is low
7. Low biological activity
8. Decreasing at the depth of the water stable aggregates (with size 1-3 mm)

6. 1. Overview of the type of Chernozems in Bulgaria
•Group of comparatively deep dark colored well structured soils
developed on the calcareous loess like materials and characterized
with mull type of humus

7. 1. Type of Chernozems in Bulgaria
Main concepts
• Chernozems have thick dark
mineral A horizon (Mollic) with
high rate of accumulation of
organic substances; with high base
saturation (> 85 %); have a
remarkable structure entirely
consisted of valuable water stable
aggregates
• Main processes that take place in
chernozems are humification,
leaching and seasonal migration of
solutions

8. Horizon
and
depth (сm)
C,
%
Organic carbon, (%) Ch/Cf Organic carbon, % Unextrac
ted
orga-
nic C,
(%)
Extracted
with
0.1N
H2
SO
4,
(%)
Extrac
ted
with
0.1N
Na
O
H,
(%)
Optic
character-
ristic
(E4/E6)
Extracted with 0.1M Na4P2O7+0.1M
NaOH
Humic acids fractions
Cext Hu-
mic acids
Ful-vic
aci
ds
“free”
and
R2O3
Ca comp
lexed
Ch
total
Ch
free
Strongly leached chernozem, none eroded and slightly eroded (1976); Endocalcic Phaeozem (Pachic, Profundihumic, Siltic) WRB (2015)
Ah
0-8
2.59 0.71а
27.41b
0.56
21.62
0.15
5.79
3.73 0.00 100 1.88
72.59
0.07
2.70
3.51 - 0.23
8.88
A1
8-24
1.97 0.59
29.95
0.45
22.84
0.14
7.11
3.21 0.00 100 1.38
70.05
0.06
3.05
3.89 - 0.15
7.61
A2
24-42
1.81 0.60
33.15
0.45
24.86
0.15
8.29
3.00 0.00 100 1.21
66.85
0.04
2.21
3.36 - 0.11
6.08
A3
42-67
1.50 0.58
38.67
0.45
30.00
0.13
8.67
3.46 0.00 100 0.92
61.33
0.04
2.67
3.30 - 0.10
6.67
AB
67-84
1.40 0.54
38.57
0.45
32.14
0.09
6.43
5.00 0.00 100 0.86
61.43
0.04
2.86
3.30 - 0.11
7.86
B1
84-105
0.93 0.38
40.86
0.21
22.58
0.17
18.28
1.23 0.00 100 0.55
59.14
0.03
3.23
3.33 - 0.07
7.53
Bk2
105-120
0.75 0.27
36.00
0.21
28.00
0.06
8.00
3.50 0.00 100 0.48
64.00
0.03
4.00
3.34 - 0.07
9.33
BCk
120-152
0.64 0.24
37.50
0.18
28.12
0.06
9.38
3.00 0.00 100 0.40
62.50
0.03
4.69
3.27 - 0.06
9.38
Ck
152-178
0.36 0.14
38.89
0.10
27.78
0.04
11.11
2.50 0.00 100 0.22
61.11
0.02
5.56
2.86 - 0.04
11.11
Ck2
178-195
0.34 0.14
41.18
0.14
41.18
0.00 - 0.00 100 0.20
58.82
0.02
5.88
3.24 - 0.04
11.76
Content and composition of soil organic matter in Strongly leached chernozem

9. Cation exchange capacity (meq/100 g soil=cmol/kg) and base saturation (%)
after the method of Ganev and Arsova (1980) in Strongly leached chernozem
0
10
20
30
40
50
60
70
80
90
100
Ah A1 A2 A3 AB B1 Bk2 BCk Ck1 Ck2
Percentage,%ofT8,2
Exch. H8.2, %
Exch. Ca, %
Exch. Mg, %
Tca, % ofT8,2
Base saturation, %
Horizon and
depth, cm
pH
H2O
CaCO3
Exchange cations,
(cmol/kg soil)
Exchange cations,
T8.2 ,(%)
Base
saturation
V %
T8.2 TCA TA H8.2 Al+H Ca Mg TCA TA H8.2
Al+
H
Ca Mg
Ah 0-8 6.35 0 43.2 36.1 7.1 4.1 0 33.0 6.1 83.56 16.44 9.49 0 76.39 14.12 90.51
A1 8-24 6.50 0 43.0 36.5 6.5 3.3 0 34.0 5.6 84.88 15.11 7.67 0 79.07 13.02 92.33
A2 24-42 6.65 0 44.70 39.3 5.4 1.6 0 37.2 5.8 87.92 12.08 3.58 0 83.22 12.98 96.42
A3 42-67 6.80 0 43.9 38.5 5.4 1.3 0 36.8 5.6 87.70 12.30 2.96 0 83.83 12.76 97.04
AB 67-84 6.70 0 39.5 33.5 6.0 2.5 0 23.2 5.5 84.81 15.19 6.33 0 81.52 13.92 93.67
B1 84-105 6.60 0 39.5 33.4 6.1 2.7 0 31.0 5.5 84.56 15.44 6.84 0 78.48 13.92 93.16
Bk2 105-120 7.35 0,76 37.4 - - 0 0 33.6 3.8 - - 0 0 89.84 10.16 100
BCk 120-152 7.35 3,12 37.3 - - 0 0 33.5 8.8 - - 0 0 89.81 10.19 100
Ck 152-178 7.60 19,4 30.5 - - 0 0 27.0 3.5 - - 0 0 88.52 11.48 100
Ck2 178-195 7.90 19,4 31.0 - - 0 0 27.5 3.5 - - 0 0 88.71 11.29 100

10. Status of Chernozems
• Historically most of the chernozems have turned to the arable
lands
• Intensive tillage practices provokes degradation of soil structure
• Erosion affects all varieties of chernozems. Detached fine soil
particles are easy prone to erosion hazard
• Subsoil became more vulnerable to compaction
• Pore space decreases resulted in the rates of aeration and water
movement through the soil
• Irrigation practices force soil negative processes related to the
degradation of structure
• Application of high rates of fertilizers together with increased
leaching reaches the deeper fosssil waters

11. Management and land use of Chernozems
• The soils quality is decisive for successful low input level of
farming
• Nutrient retention capacity against losses caused by leaching
determined by the rate of drainage of soil and loads with fertilisers
• Rooting conditions of available penetrability for roots to extract
nutrients are favourable for most of crops
• Oxygen availability defined by drainage characteristics and terrain
characteristics
• Chernozems soils are easy to work independent of moisture
conditions
• Irrigation practices force soil negative processes and provoke
secondary salinezation at some sites

12. 2. Overview of the type of Smolnitsa in Bulgaria
Group of comparatively deep not differentiated black colored clayey soil
throughout, where the high shrinking and swelling activity produces
specific gilgai microrelief

13. 2. Type of Smolnitsa in Bulgaria
Main concepts
Smolnitsa is a mineral soil
characterized with intensive black
color and (Pellic) horizon;
With comparatively low content of
organic matter;
High (> 30 %) clay content;
Soil is base saturated (> 90 %);
Main processes have taken place are
self-pedoturbation due to high
shrinking-swelling activity and
leaching

14. Status of land use of Smolnitsa
• Historically smolnitsa was problematic for
agricultural use, because of tillage drawback
• Soils become very hard-setting during the dry
period and are very plastic and sticky during the wet
period
• The over limitation is a short tillage period
• The repeated cultivation caused deterioration of soil
structure
• Irrigation practices forced soil negative processes
and provokes secondary salinity at some sites

15. Management and land use of Smolnitsa
• The soils quality is successful to some extent intermediate (to high)
input levels of farming
• Plant nutrients are held in Smolnitsa on the exchange sites provided
by the clay fraction and the clay-humus complex
• Losses vary determined by the rate of drainage of soil moisture
through the soil profile
• Rooting conditions to extract nutrients are limited by presence of
shrinking and swelling properties (vertic) affecting root and tuber crops
• Oxygen availability in soils is largely defined by drainage
characteristics and takes into account soil texture and terrain slope
• Workability constraints are for intermediate and high inputs of
farming. Smolnitsa is only manageable at an adequate moisture status, in
particular for light machinery
• Oil conditions are foremost affecting mechanized land preparation
and harvesting operations are of high-level input mechanized farming

16. Soil group after
Extended
Systematic List,
1976
WRB 2006, (Name) WRB 2015, (Name) Soil Taxonomy
USDA 2014, (Name)
Revised Legend of
the World Soils
FAO-UNESCO, 1990
Calcareous
and Typical
chernozems
Epicalcic Kastanozem
Epicalcic Chernozem
Epicalcic Chernozem
(Pachic)
Epicalcic Kastanozem
(Siltic)
Epicalcic Chernozem
(Siltic)
Calcic Haploxerepts
Typic Calcixerolls
Pachic Calcixerolls
Calcic Chernozems
Slightly leached and
Medium leached
chernozems
Epicalcic Chernozem
Endocalcic Chernozem
Endocalcic Chernozem
(Siltic)
Calcic Haploxerolls
Typic Haplustolls
Calcic Chernozems
Strongly leached
chernozems
Bathycalcic Chernozem Haplic Chernozem
(Bathyprotocalcic,
Siltic)
Typic Haplustolls Haplic Chernozems
Leached heavy
chernozems
Endocalcic Vertic
Chernozem (Clayic)
Endocalcic Vertic
Chernozem (Clayic)
Vertic Haplustolls Verti-Haplic
Chernozem
Podzolized
(degraded)
chermozems
Luvic Chernozem Greyic Luvic Greyzemic
Chernozem
(Bathyprotocalcic,
Siltic)
Typic Argialbolls Luvic Chernozems
Calcareous
and Typical
Smolnitsa
Epicalcic Mollic Grumic
Vertisol Calcaric
Epicalcic Vertisol
(Mollic)
Typic Calcixererts Calcic Vertisols
Slightly and Medium
leached smolnitsa
Epicalcic Mollic Grumic
Vertisol Calcaric
Pellic Endocalcic
Vertisol (Grumic)
Typic Calciusterts Haplic Vertisols
Strongly leached
smolnitsa
Bathycalcic Mollic
Grumic Vertisol Pellic
Pellic Vertisol (Bathy-
protocalcic, Grumic)
Pachic Vertic
Haplustolls
Haplic Vertisols