COMPARISON BETWEEN ORGANIC MATTER CONTENT OF MAIN SOIL ORDERS IN KURDISTAN REGION USING TWO DIFFERENT METHODS.*

Abstract

This study was conducted to compare between two methods of soil organic matter determination for main soil orders in Kurdistan region/Iraq, for this purpose forty-five soil samples were taken then the organic matter was determined using chemical (Walkley-Black (wet) method and loss-on-ignition method (dry) combustion method. The results indicated the significant correlation (r = 0.88**) between the studied methods It means there is good adjustment to convert organic matter by loss-on-ignition method (dry) to Walkley-Black (wet) method organic matter by this linear equation (organic matter by loss-on-ignition =1.651* Walkley-Black method organic matter +2.1877) this equation can be used to convert organic matter by two methods for Mollisols(M), Vertisols(V) and Aridisols(A) in Hawler(H), Sulaimani(S) and Duhok(D) governorates, this equation is very important and economic to determine and convert dry method to wet method, the amount of organic matter for M, V, A was recorded the highest value (49.5, 24.8, 20 gkg-1) respectively for Mollisols, Vertisols, and Aridisols at Hawler (H), Sulaimani (S), and Duhok(D) respectively for (DM5, SV4, DA1) in Duhok Mollisols, Sulaimani Vertisols and Duhok Aridisol respectively for walk- black (wet) method, the highest value for dry method organic matter in Mollisols, Vertisols, Aridisols was recorded (97.6, 77.9, 50.3 g kg-1) for soil orders (MD3, VD4, AD4) respectively.

Full text

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
1
COMPARISON BETWEEN ORGANIC MATTER CONTENT OF MAIN
SOIL ORDERS IN KURDISTAN REGION USING TWO DIFFERENT
METHODS.*
M. R. Khoshnaw1 A. O. Esmail 2
Assist. lecturer Professor
Dept. Soil and Water. Coll. Agric. University of Salahaddin, Erbil
muslim.khoshnaw@su.edu.krd akram.esmail@su.edu.krd
ABSTRACT
This study was conducted to compare between two methods of soil organic matter determination for
main soil orders in Kurdistan region/Iraq, for this purpose forty-five soil samples were taken then the
organic matter was determined using chemical (Walkley-Black (wet) method and loss-on-ignition
method (dry) combustion method. The results indicated the significant correlation (r = 0.88**)
between the studied methods It means there is good adjustment to convert organic matter by loss-on-
ignition method (dry) to Walkley-Black (wet) method organic matter by this linear equation (organic
matter by loss-on-ignition =1.651* Walkley-Black method organic matter +2.1877) this equation can
be used to convert organic matter by two methods for Mollisols(M), Vertisols(V) and Aridisols(A) in
Hawler(H), Sulaimani(S) and Duhok(D) governorates, this equation is very important and economic
to determine and convert dry method to wet method, the amount of organic matter for M, V, A was
recorded the highest value (49.5, 24.8, 20 gkg-1) respectively for Mollisols, Vertisols, and Aridisols at
Hawler (H), Sulaimani (S), and Duhok(D) respectively for (DM5, SV4, DA1) in Duhok Mollisols,
Sulaimani Vertisols and Duhok Aridisol respectively for walk- black (wet) method, the highest value
for dry method organic matter in Mollisols, Vertisols, Aridisols was recorded (97.6, 77.9, 50.3 g kg-1)
for soil orders (MD3, VD4, AD4) respectively.
Keywords: methods of determination , soil texture, Calcium Carbonate.
*Part from Ph.D. dissent a form of the 2nd author
- )18 



 

       )Walkley-Black
(wetr = 0.88

 
Walkley-
Black (wet))(             
Walkley-Black           
Mollisols (M)Vertisols (V)Aridisols (A)HSD


M VA     ( 

 MVA
DM5SV4 DA1Walkley-Black (wet))(
M V A 97.6) 77.9 50.3 

 MD3 VD4AD4

*Received:17/3/2019, Accepted:19/6/2019

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
2
INTRODUCTION
Iraqi soils illustration different degrees of
development according to the dominant local
conditions mainly climatic and geological
conditions. The results of the morphological,
physical and chemical soil properties indicated
to the presence of five soil orders including
Aridisols, Entisols, Inceptisols, Mollisols, and
Vertisols. Each order shows some variations
within the common properties reflecting the
effect of the dominant local conditions mainly,
climatic and type of parent materials (17).
These orders arranged according to their
percentage from the total Iraqi area as follow:
Aridisols (62.2 %), Entisols (16.2%),
Inceptisols (12.6%), Mollisols (3.8%) and
Vertisols (1.2 %) respectively in Kurdistan
regain the dominant orders are Mollisols,
Aridisols and Vertisols. When plant residues
are returned to the soil, various organic
compounds undergo decomposition.
Decomposition is a biological process that
includes the physical breakdown and
biochemical transformation of complex
organic molecules of dead material into
simpler organic and inorganic molecules (3)
Organic matter plays important roles in
improving soil physical, chemical, and
biological properties. It is considered as a very
important parameter of soil fertility and
productivity. It provides nutrients to the soil,
improves water holding capacity and helps the
soil to maintain better aeration and soil quality
for seed germination and plant root
development (3,21,30). Soil organic matter is
considered to be a key influence of soil quality
because of its effect on the chemical, physical,
and biological properties and processes in
soils. Conversely, it is not sensitive to short-
term changes of soil quality with different soil
or crop management practices due to high
background levels and natural soil variability,
it has been suggested by (14,5). Soil organic
matter plays an important role in nutrient
cycling in tropical ecosystems as well as
important for the maintenance of soil structure
and fertility (20,24,25,26). Soil organic matter
encompasses a diversity of organic
compounds with decomposition rates which
vary continuously due to the complex
interactions of biological, chemical and
physical processes in soils (11). It is well
known the importance of soil organic matter
for soil quality and plant growth. Thus, several
methods have been proposed for its
measurement (15,27) and several papers
discussed the most common ones. The
establishment of the relationship among
different methods of organic carbon
determination is important for soil carbon
(12,22). There are little or no studies about the
correlation between the methods of organic
matter determination for this reason this study
was selected to explain the statistical
relationship between them. The objective of
this study the correlation between soil organic
matter content in Kurdistan region using two
different methods in different dominant soil
orders (Mollisols(M), Vertisols(V) and
Aridisols(A)) in Hawler(H), Sulaimani(S) and
Duhok(D) in Kurdistan region.
MATERIALS AND METHODS
Three dominant of (soil orders) were collected
from Hawler, Sulaimani and Duhok
governorates fifteen samples in each order
were taken from the soil surface (0-30) cm
depth to determine the equation to convert
organic matter by Walkley–Black method to
organic matter by on-ignition method (dry
method) or Versa. Forty-five soil samples
were taken on November, 2016 from the soil
surface (0-30) cm depth for the dominant soil
orders (Mollisols, Aridisol and Vertisols ) in
Hawler, Sulaimani and Duhok governorates,
fifteen samples were taken in each
governorate (5 samples per soil order) were
air-dried, thoroughly mixed, and sieved using
2mm sieve for soil physical and chemical
analysis. The soil analysis included Electrical
Conductivity (EC) depending on (23), calcium
carbonate (CaCO3) depending on., (7),
Moisture content according to (10), and field
capacity (FC) and wilting point (W.P) were
determined according to the models prepared
by (8) Particle size distribution was
determined by hydrometer method as
mentioned by (10). using sodium
hexametaphosphate (Calgon) as the dispersing
agent. Soil pH of the saturated extract was
measured with pH-meter; model 332
JENWAY, as mentioned by (16).Soil organic
matter calculated as the loss-on-ignition
method reported by (29). The parameters
measured were determined, and the analysis

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
3
was carried out at the soil and water
department laboratories, in Agriculture
College, at Salahaddin University. Three
orders Kurdistan regain soil samples,
including Mollisols, Vertisols, Aridisols
illustrated in (Table 1)
RESULTS AND DISCUSSION
Table 1 illustrates some physic-chemical
properties of the studied soils such as soil
texture, water content, field capacity,
saturation past, calcium carbonate, pH, and
electrical conductivity for dominate orders in
Kurdistan region Table 1 shows the physic-
chemical properties of for Mollisols, Vertisols,
and Aridisols in Hawler, Sulaimani, and
Duhok, respectively. The results of the
numerical simulation indicate that the soil
texture for Mollisols, Hawler and Sulaimani
were silty loam the amount of particle size
distribution for ( sand, silt, and clay) were
(230, 560, 200) g kg-1 and (114.1, 455.9, 430)
g kg-1 in Hawler and Sulaimani respectively,
whereas in Duhok was silty clay, the sand, silt,
and clay were (176.2, 396.3, 427.5) g kg-1. As
well as the soil texture of Vertisols in Hawler,
Sulaimani and Duhok were silty clay, and
amount of sand, silt, and clay were (452.4,
71.9, 475.7) g kg-1, (43.2, 400.5, 556.3) g kg-1
and (35, 455.8, 509.2) g kg-1 respectively,
while the soil texture for Aridisols in Hawler
and Duhok were clay loam with particle size
distribution of (220.2,509.6, 270.2) g kg-1 and
(221.1, 413.6, 365.3) g kg-1 for sand, silt, clay
respectively, but for Sulaimani was silty clay
loam the amount of sand silt and clay were (
143.7, 541.8, 314.5) g kg-1 for sand, silt and
clay, respectively, results showed that the
increase of clay percentage cause increasing in
water content as mentioned by (6) Percentage
water content (WC), field capacity, (FC),
wilting point (W.P), saturation past (SP),
calcium carbonate (CaCO3 g kg-1), pH, and
electrical conductivity (EC dSm-1 ) were (5.05,
21.25, 11.59, 39.52, 300, 7.394, 0.36 dSm-1)
respectively for Hawler Mollisols, while for
Sulaimani Mollisols were (6.0, 30.35, 19.62,
56.45, 230, 7.308, 0.54 dSm-1) was recorded
respectively on the other hand. Duhok
Mollisols were (4.86, 30.25, 19.53, 56.27,
214, 7.536, 0.48 dSm-1) respectively, so
Hawler Vertisols were (4.24, 32.17, 21.22,
59.83, 300, 7.474, 0.4 dSm-1) respectively,
Sulaimani Vertisols were (4.71, 35.37, 24.04,
65.78, 268, 7.464, and 0.29 dSm-1)
respectively. Duhok Vertisols were (9.20,
33.50, 22.39, 62.30, 240, 7.472, and 0.36 dSm-
1). Hawler Aridisols were (2.34, 24.01, 14.03,
44.65, 488, 7.45, and 0.5 dSm-1) respectively.
Sulaimani Aridisols were (3.78, 25.76, 15.58,
47.92, 460, 7.472, and 0.52 dSm-1)
respectively. Duhok Aridisols were (2.89,
27.78, 17.35, 51.67, 590, 7.492, and 0.4 dSm-
1) respectively. (21,18) said that the soil
organic matter has an important effect on the
physicochemical status. Increase the amount
of organic matter in the soil improve the
physical and chemical properties (3,9,19). The
relation between the two methods was
significantly reported by (22,29) It has been
suggested that soil organic matter is
considered to be a key influence of soil quality
because of its role on chemical, physical, and
biological properties and processes in soils
The results indicated that there was a
significant correlation between two methods
using in the determination of organic matter
with the correlation coefficient value of
(r=0.8819**) (organic matter by loss-on-
ignition method =1.651* Walkley-Black
method organic matter + 2.1877) y = organic
matter by muffle method, X= Walkley-Black
method organic matter this equation can be
used for convert organic matter by two
methods in Mollisols, Vertisols, and Aridisols
for Hawler, Sulaimani, and Duhok, in another
hand this equation is very important and
economic to determine and convert organic
matter by the dry method to wet method
shown in Figure 1 The figure provides
information about the correlation between two
methods Walkley-Black method and loss-on-
ignition method for determining organic
matter Mollisols, Vertisols, and Aridisols in
Kurdistan region. This figure shows a
significant correlation ( r=0.8819**) between
two methods (Walkley-black) loss-ignition)
used in determining organic matter in this
soils, as well as the Paired Samples Statistics,
are significant for Mollisols, Vertisols, and
Aridisols in each order, the highest value for
organic matter was recorded in Duhok
Mollisols (49.5 g kg-1) for wet method
(Walkley-Black) while the lowest value (38.3
g kg-1) was recorded in Hawler Mollisols

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
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(HM2), as well as the highest value (97.6 g kg-
1) for muffle method (dry method) was also in
Duhok Mollisols (DM3), whereas the lowest
value (80.9 g kg-1) found in Sulaimani
Mollisols (SM1). The highest value was
recorded for organic matter in Sulaimani
Vertisols (SV4) was ( 24.8 g kg-1) for wet
method Walkley-Black, while the highest
value for the dry method was recorded in
(DV4) was (77.9 g kg-1), where the lowest
value (20.4 g kg-1) for Vertisols was recorded
in Duhok Vertisols for wet method Walkley-
Black, as well as the highest value for muffle
method (dry method) in Duhok Vertisols
(DV3) was (96.1 g kg-1), so the lowest value
(5.32%) was recorded in (HV3) in Hawler
Vertisols for dry method. The highest value
was recorded for organic matter in Duhok
Aridisols (DV1) was (20. g kg-1) in (DA1) for
wet method Walkley-Black, while the lowest
value in Sulaimani Aridisols (SA5) was (12.9
g kg-1) for wet method Walkley-Black, as well
as the highest value for muffle method was
(50.3 g kg-1) Duhok Aridisols in (AD4) for dry
method, whereas the lowest value was
recorded in Sulaimani Aridisols (SA2) was
(26.3 g kg-1) in (SA2). All results were shown
in table (2) the amount of calcium carbonate
was recorded in Aridisols was (590 g kg-1) in
Duhok, while the lowest value for organic
matter in Aridisols Sulaimani was (12.9) for
chemical method and (26.3) for dry method,
pH values were around (8) in most of the soils
due to the high calcium carbonate content.
Total organic carbon contents were generally
low because of the semiarid climatological
characteristics by low rainfall and high
temperatures according to (2), soil organic
matter is a very important source of nutrient
(11) the impact of feeding different particle
sizes of CaCO3 on weight grain and feed
conversions of broilers has not been studied
extensively. (4) all results illustrated in the
table (2).
Figure 1. correlation between Walkley-Black and loss-on-ignition method for determine
organic matter in dominat soil orders (Mollisols, Vertisol, Aridisol) in Hawler, Sulaimany
and Duhok

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
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Table 1 Mean for some chemical and physical properties for dominant soil orders Mollisols,
Vertisols, Aridisol in Hawler, Sulaimani and Duhok.
Treatment
Particle Size Distribution g kg-1
WC%
FC
W P
SP
CaCO3
pH
EC
%
g kg-1
dS m-1
Hawler
Mollisols
Sand
230
Silty loam
5.05
21.25
11.59
39.52
300
7.394
0.36
Silt
560
Clay
200
Sulaimany
Mollisols
Sand
114.1
Silty loam
6.00
30.35
19.62
56.45
230
7.308
0.54
Silt
455.9
Clay
430
Duhok
Mollisols
Sand
176.2
Silty clay
4.86
30.25
19.53
56.27
210
7.536
0.48
Silt
396.3
Clay
427.5
Hawler
Vertisols
Sand
452.4
Silty clay
4.24
32.17
21.22
59.83
300
7.474
0.41
Silt
71.9
Clay
475.7
Sulaimani
Vertisols
Sand
43.2
Silty clay
4.71
35.37
24.04
65.78
268
7.464
0.29
Silt
400.5
Clay
556.3
Duhok
Vertisols
Sand
35.0
Silty clay
9.20
33.50
22.39
62.30
240
7.472
0.36
Silt
455.8
Clay
509.2
Hawler
Aridisol
Sand
220.2
Clay loam
2.34
24.01
14.03
44.65
488
7.45
0.5
Silt
509.6
Clay
270.2
Sulaimani
Aridisol
Sand
143.7
Silty clay
loam
3.78
25.76
15.58
47.92
460
7.472
0.53
Silt
541.8
Clay
314.5
Duhok
Aridisol
Sand
221.1
Clay loam
2.89
27.78
17.35
51.67
590
7.492
0.4
Silt
413.6
Clay
365.3

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
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Table 2. The soil organic matter content of the studied soil samples using Walkley-Black and
muffle methods for determine organic matter in Hawler, Sulaimani, Duhok, for two different
methods
Soil sample
Organic matter
g kg-1
Location
No.samples
Walkley-Black (wet)
loss-on-ignition method (Dry)
Hawler
Mollisols
1
39
89.6
2
38.3
87.3
3
39.1
84.8
4
39.5
86.8
5
39
82.4
Sulaimani
Mollisols
1
43
80.9
2
41.8
91.6
3
40.7
90.1
4
41.8
90
5
41.7
91.8
Duhok
Mollisols
1
42.7
90.7
2
40.4
90.6
3
43.8
97.6
4
42.7
92.7
5
49.5
97.1
Hawler
Vertisols
1
21.2
59.8
2
24.1
62.3
3
24
53.2
4
22.9
57.4
5
23.9
67.1
Sulaimani
Vertisols
1
23
67.6
2
24.4
69.6
3
21.5
71.1
4
24.8
72.7
5
21.6
71.5
Duhok
Vertisols
1
20.5
75.4
2
21.3
74.2
3
20.4
73.6
4
20.5
77.9
5
21.6
74.9
Hawler
Aridisol
1
18.7
46
2
16.1
49.5
3
17.5
41.5
4
18.2
46.6
5
18.7
40.2
Sulaimani
Aridisol
1
14.2
28.6
2
15.8
26.3
3
14
36.3
4
14.6
28.9
5
12.9
44
Duhok
Aridisol
1
20
49.6
2
18.9
47.8
3
14.3
41.6
4
17.7
50.3
5
18.1
46.9
CONCLUSION
The results of determining the organic matter
in the main soil orders Mollisols, Vertisols and
Aridisols (M, V, A) in Hawler, Sulaimani, and
Duhok for Kurdistan region using wet and dry
methods was recorded the significant
correlation coefficient between them
(r=0.882). The regression equation between
the studied methods the analysis shows that
correlation between soil organic matter

Iraqi Journal of Agricultural Sciences –:51(Special Issue):1-8  Khoshnaw & Esmail
7
content for soil orders in Kurdistan region
using two different methods was a significant
with correlation coefficient value of (r=0.882),
and determine the amount of organic matter to
three dominant orders in the surface (0-30
cm), also determine the equation for estimate
organic matter in three orders convert organic
by the wet method to dry method and versa by
linear equation. The best for determination of
the organic matter is the wet method cause
more accuracy. Result illustrated that
recommended to determine the organic matter
by this equation (organic matter loss-on-
ignition method =1.651* organic
matter(Walkley-Black method) + 2.1877) this
is the economic method to determine the
organic matter by wet or dry
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