Journal of Environmental Biology
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September 2008, 29(5) 677-682 (2008)
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Effect of modifying land cover and long-term agricultural practices on the soil
characteristics in native forest-land
Ceyhun Gol1 and Orhan Dengiz*2
1
Forestry Faculty, Ankara University, Cankiri - 18200, Turkey
Department of Soil Science, Agricultural Faculty, Ondokuz Mayis University-55139, Samsun, Turkey
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2
(Received: June 26, 2007; Revised received: August 21, 2007; Accepted: September 10, 2007 )
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Abstract:Natural forestland soils in the high land mountain ecosystems on the eastern Black sea region of Turkey are being seriously degraded and
destructed due to intensive agricultural practices. In this study, we examined four soil profiles selected from four sites in each of three adjacent land use types
which are native forest, pasture and cultivated fields with corn and hazelnut to compare the soil physical, chemical and morphological properties modified after
natural forestland transformation into cultivated land. Disturbed and undisturbed soil samples were collected from four sites. The effects of agricultural
practices on soil properties taken from each three adjacent land use types were most clearly detected in the past 50 years with the land use change. Land
use change and subsequent tillage practices resulted in significant decreases in organic matter, total porosity, total nitrogen and reduced soil aggregates
stability. However, contents of available P were improved by application of phosphorous fertilizers in cultivated system. There was also a significant change
in bulk density among cultivated, pasture and natural forest soils. Depending upon the increase in bulk density and disruption of pores by cultivation, total
porosity decreased accordingly. The data show that long term continuous cultivation of the natural forest soils resulted in changes in physical and chemical
characteristics of soils.
Key words: Natural forest-lands, Long-term cultivation, Land use change, Soil properties
PDF of full length paper is available with author ( *[email protected])
provoke soil erosion (Williams, 1993). Pore size distribution and
hydraulic connectivity together with bulk density, aggregation are
important soil physical properties that can be to a great extent
influenced by the land degradation due to the land cultivation (Celik,
2005; Cerda, 1996). Aggregation and aggregate stability are also
directly linked to soil erodibility in the surface soils. Soil loss is
accelerated by soil degradation, especially, soil compaction that
induces organic matter losses, low infiltration and high runoff (Durak
et al., 2006) because of the use of heavy tillage. Therefore, soils
become more sensitive to soil erosion since soil structure and
aggregates are disrupted (Six et al., 2000).
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Introduction
Variation of land cover and management practices,
implemented locally such as long term cultivation, deforestation,
overgrazing and mineral fertilization can cause significant
modifications in soil characteristics (Shepherd et al., 2000; Chen et
al., 2001; Braimoh and Velk, 2004; Jiang et al., 2006). The
conversion of native forest into other forms likes pasture or crop
lands are of considerable concern worldwide in the context of
environmental degradation and global climate change (Mahtab and
Karim, 1992; Wail et al., 1999; Celik, 2005). Under similar ecological
environments human land use and management measures become
the dominant factors affecting soil properties and crop production
(Nnaji et al., 2002; Onweremadu, 2007). Akamigbo (1999), reported
that soils formed over the same parent material and under the same
climate and relief had dissimilar bulk densities due to cultivations.
Additionally, land use changes such as conversion of the natural
forest to arable agriculture lands are known to result in loss of
organic matter associated with organic carbon and nitrogen content
(Houghton et al., 1999; Osher et al., 2003; Solomon et al., 2002;
Sharma et al., 2004; Henrot and Robertson, 1994). Elliott (1986)
and Grupta and Germida (1988) reported that cultivation of pasture
soils has resulted in 25-50% decrease in soil organic carbon.
Similar result was also found by Jiang et al. (2006). In their study,
they indicated that soil organic matter content decreased from 38.02 to
25.76 g kg-1 in the past 20 years (1982-2003) after transformation
of forestland into cultivated land. These changes in organic matter
content following land transformation can connect distribution and
stability of soil aggregates (Paustian et al., 2002; Elliott, 1986) and
Soils and forest are highly interrelated and none of them
can live without each other. The forest covers and protects the soil
from natural forces. Soils sustain the forest and provide raw materials
for its life by recycling fallen leaves, woody debris, and dead animals
(Barreto et al., 2000; Misir et al., 2007). The soil provides main
needs to trees like mixture of air, water, decaying organic and
inorganic material and billions of living organisms within the
surrounding ecosystem. Land use changes such as forest clearing,
cultivation and pasture introduction are known to result in changes
in soil chemical and physical properties (Houghton et al., 1999), yet
the sign and magnitude of these changes varies with land cover
and land management (Baskin and Binkley, 1998; Hu et al., 1997;
Van Noordwijk et al., 1997).
According to the current forest inventories and forest
management plans (1973-1999), Turkey covers approximately
total 77.9 million hectare of land (Mha) whose 20.7 Mha is forest,
Journal of Environmental Biology
September, 2008 678
Ceyhun Gol and Orhan Dengiz
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41 N
o
27 E
BLACK
SEA
o
41 N
o
43 E
The study area
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ANKARA
o
36 N
o
43 E
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36 N
o
27 E
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Fig. 1: Location of the study area
which corresponds about 26.6% of Turkey’s total land area. But only
about half of the existing forests (9 Mha) are classified as normal
(productive) forest and the other half (11 Mha) as degraded or severely
degraded forest (TMEF, 2006; Esen and Yildiz, 2006). Turkey with
the elevation of 1500 m and higher, and slope range of 15-40%
account for about 26 and 34% of the total land area, respectively
(Atalay, 1997). The greatest part of forestland also lies within high
land mountain ecosystems in Turkey. However, increasing public
demand for various needs has led to the conversion of natural
Journal of Environmental Biology
September, 2008 forestlands to other uses (Yener and Koc, 2006). However, this case
put ecological sustainability of the natural resources at risk in northern
Anatolian mountain forestland located on Blake sea region of Turkey.
The objective of this study was to determine some chemical and
physical soil properties modified after forestland transformation into
cropland and pasture in a eastern Black sea highland region of
Turkey. In this study, the changes in the properties of soils include
organic matter, available phosphorous and nitrogen content, bulk
density, total porosity, hydraulic conductivity and aggregate stability.
679
Effect of modifying land cover and long-term agricultural practises on soil
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After disturbed soil samples were then air-dried and passed
through a 2 mm sieve, particle size distribution was determined by
the hydrometer method (Bouyoucos, 1962). A wet sieving method
was used to determine the percentage of aggregate stability (water
stable aggregates, WSA%) Kemper and Rosenau (1986). Soil
organic carbon was measured by wet digestion (Nelson and
Sommers, 1982). Values of soil organic carbon were multiplied by
a factor 1.72 to obtain soil organic matter. pH, electrical conductivity
(of the saturation) by method of the (Soil Survey Laboratory, 1992).
Total N and available P forms were determined by Kjeldahl (Bremner
and Mulvaney, 1982) and Bray and Kurtz (1945) methods.
Statistically analysis: All data were analyzed using TARIST
statistical software. Analysis of variance (ANOVA) was carried out
using two-factor randomized complete plot design; where significant
F-values were obtained, differences between individual means
were tested using the LSD (Least Significant Difference) test, with a
significance level of p<0.01. The asterisks, *, ** and *** indicate
significance at p<0.05, 0.01 and 0.001, respectively.
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Materials and Methods
Description of the study field: The study area is located in
Ordu-Ulugol watershed, which extend from 40o 321 to 40o 501 N
latitude and has an elevation of about 1400 m above sea level
within longitude 37o 271 and 37o 451 E in eastern Black sea highland
region of Turkey (Fig. 1). Ulugol watershed covers 26.3 ha and
7.5 ha of total area is Ulugol lake. Ulugol is a tectonic lake and
around the lake has been used as natural recreation and festival
places for two decades (Gol et al., 2006). According to Thorntwaite
(1948), the prevailing climate of the study area is moist, megathermal, humid climate that has intensive water surplus in winter and
that was coded with BA’rS2. The long-term mean annual temperature
and precipitation were 8.4oC and 1683 mm, respectively.
Topography and slope show great variations and hilly and rolling
physiographic units are particularly common in the study area. The
research area is located in the European-Siberian flora zone that is
one of the three major flora zones of Turkey and lies in the A6
square according to the Davis’s grid system (Davis, 1965).
Dominant tree species of natural forest are oriental beech (Fagus
orientalis Lipsky) and birch hornbeam (Carpinus betulus L.) in
Ulugol watershed. Some part of natural forest has been fragmented
and degraded by such human disturbances as clearance for
agriculture and pasture. Forest has been cultivated at least 50
years with corn, vegetable and especially hazelnut in a rational
manner.
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Turkey is responsible for about 70% of world hazelnut
production and 75% of world hazelnut trade (Ayfer et al., 1986;
Reis and Yomralioglu, 2006).The production area is spread densely
all along the Black sea coast. Ordu province is one of the Turkey’s
most important hazelnut production centers. 28% of Turkey’s
hazelnut production has been produced in this province (Kilic and
Demir, 2004). However, most of the hazelnut orchard places have
been generally converted from natural forest land.
Results and Discussion
Soil morphology and classification: Field morphology and
physico-chemical characterizations data for representative profiles
of the soils are presented in Tables 1 and 2. Soils selected from
pasture and cultivated fields modified from natural forest display
variation in terms of particle distribution, structure, color, organic
matter and depth in surface horizon. These variables are the obvious
effect of agricultural practices and erosive forces. Litter layer formed
about 8 cm thick on the uppermost soil horizon of natural forest land
and its adjacent continuously cultivated lands have lower organic
matter due to high decomposition. In addition, soil color of the natural
forest clearly distinct from the underlying horizons is darker than
other land use types. Textural and organic matter changes have
also effects structural development of soils. While owing to loss of
organic matter and slight texture, structural developing of cultivated
and pasture land soils are weak and fine granular (Fig. 1), maximum
structural formation was observed in natural forest land (Table 1). It
is because, organic matter including humic materials that are
responsible for stabilizing and strengthing of soil structure.
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Soil sampling and analysis: Four soil profiles were selected for
this study from four sites in each of three adjacent land use types
which are native forest, pasture and cultivated fields with corn and
hazelnut. These adjacent four profiles locate on the similar aspect,
elevation and slope. Morphological properties of these four soil
profiles in the field were identified and sampled by genetic horizons
and classified according to Soil Survey Staff (1993, 1999). 17
disturbed and 14 undisturbed soil samples were taken to investigate
for their physical and chemical properties at the laboratory. Disturbed
soil samples were then air-dried and passed through a 2 mm sieve
to prepare for laboratory analysis.
Undisturbed soil samples were taken by using a steel core
sampler of a 100 cm volume. Bulk density and total porosity were
determined with the undisturbed soil samples. Dry bulk density was
determined by the core method (Blake and Hartge, 1986). Total
porosity was calculated in undisturbed water-saturated samples of
100 cm3 assuming no air trapped in the pores and validated using
dry bulk density and a particle density of 2.65 g cm-3 (Danielson
and Sutherland, 1986)
The soils were classified according to the criteria proposed
by the Soil Taxonomy (1999) based on morphological, physical
and chemical characteristics. According to the meteorological data,
the study area has udic soil moisture regime and mesic temperature
regime (TSMS, 1993). All soils were classified as Inceptisolls in
order level, but these soils have mollic, cambic and lithic surface
and subsurface horizons leading to their classification as Typic
Dystrudept, Mollic Dystrudept, Lithic Dystrudept in sub-group level
located on pasture-corn fields, natural forest and hazelnut cultivation
lands, respectively.
Soil characteristic change: Table 2 reveals that soil characteristics
have changed in the past 50 years with the land use change.
Conversion of the natural forest into continuous cultivation had resulted
in statistically significant decreases of both the concentration and
Journal of Environmental Biology
September, 2008 680
Ceyhun Gol and Orhan Dengiz
Table - 1: Morphological description and classification of soil profiles
Profile 2
Natural forest
Profile 3
Hazelnutcultivation
Profile 4
Corn cultivation
Matrix color dry - moist
Structure
Consistence
Boundary
Roots
0-7
7-23
23-44
44-70
70+
10 YR 4/3, 10 YR 4/4
10 YR 5/3, 10 YR 5/4
10 YR 5/2, 10 YR 5/3
10 YR 5/3, 10 YR 5/4
10 YR 5/4, 10 YR 6/4
2 mgr
1 fgr
2 msbk
massive
massive
sh fr
sh vfr ss ps
sh fr ss ps
sh fr ss ps
sh vfr ss ps
aw
cw
cw
cs
-
3 vfm
2 fm
1m
1 co
-
0-8
8-22
22-40
40-70
70+
10 YR 3/1, 10 YR 3/2
10 YR 4/3, 10 YR 4/2
10 YR 4/3, 10 YR 4/3
10 YR 5/3, 10 YR 5/4
10 YR 5/3, 10 YR 5/4
2 mgr
2 mgr
2 msbk
massive
massive
sh fi ss ps
sh fi ss ps
sh fi ss ps
sh fr ss ps
sh fr ss ps
cw
cw
cw
cw
-
3 vfm
2 mco
2 mco
1 mco
1 co
0-20
20-32
32+
7.5 YR 4/3, 7.5 YR 4/4
7.5 YR 5/2, 7.5 YR 5/3
7.5 YR 5/3, 7.5 YR 5/3
1 fgr
2 fsbk
massive
sh fr ss ps
sh fr ss ps
so fi ss ps
aw
cw
-
2 fm
2m
1 co
0-16
16-35
35-53
53+
10 YR 4/4, 10 YR 4/3
10 YR 4/2, 10 YR 4/2
10 YR 5/3, 10 YR 5/4
10 YR 6/2, 10 YR 6/3
1 fgr
2 fsbk
massive
massive
so fi ss ps
h fi ss ps
sh fr ss ps
sh fr ss ps
aw
cw
cw
-
2 vfm
1 fm
-
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Profile 1
Pasture
Depth (cm)
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Land use type
Abbreviations: Boundary: a = abrupt, c = clear, g = gradual, d = diffuse, s = smooth, w = wavy, i = irregular, Structure: 1 = weak, 2 = moderate,
3 = strong, vf = very fine, f = fine, m =medium, c = coarse, gr = granular, pr = prismatic, abk = angular blocky, sbk = subangular blocky.
Consistence: (Dry) lo = loose, so = soft, sh = slightly hard, h = hard, (Moist) lo = loose, vfr = very friable, fr = friable, fi = firm, (Wet) so = nonsticky,
ss = slightly sticky, st= sticky, po = nonplastic, ps = slightly plastic, pt= plastic, Roots: 1 = few, 2 = common, 3 = many, vf = very fine, f = fine, m = medium,
co = coarse
Table - 2: Selected physical and chemical properties for four representative profiles of land use types
Profile 1
Pasture
pH
0-7
7-23
23-44
44-70
70+
Profile 3
Hazelnut cultivation
Profile 4
Corn cultivation
Particle size (%)
EC
dS.m-1
OM
(%)
TN
(g kg-1)
AP
(g kg-1)
Sand
Silt
Clay
6.53c
6.80b
5.50d
5.09e
7.24a
1.04c
0.97d
1.10b
1.10b
1.17a
3.19b
3.44a
1.83c
0.85d
0.72e
0.259
0.172
0.092
0.043
0.036
0.36b
0.39a
0.33c
0.23e
0.30d
33
72
27
30
27
44
7
48
46
47
23
21
24
24
26
1.29a
1.23b
1.01c
-
0.513
0.536
-
75.4a
65.8b
62.6c
-
0-8
8-22
22-40
40-70
70+
5.09e
6.88a
5.11d
5.28c
5.34b
1.07a
1.03c
1.07a
1.06b
1.01d
6.29a
3.24b
1.05e
1.54c
1.07d
0.315
0.162
0.053
0.077
0.054
0.36c
0.57a
0.22e
0.39b
0.33d
28
32
30
28
29
45
46
46
44
40
27
22
24
27
31
0.77c
1.01b
1.07a
-
0.709
0.619
-
87.5b
88.4a
81.7c
-
0-20
20-32
32+
6.90b
7.34a
6.34c
1.35a
1.13c
1.22b
2.05a
1.74b
1.13c
0.152
0.138
0.082
1.76a
0.56b
0.29c
32
34
36
44
42
34
24
24
30
1.21b
1.23a
—
0.543
0.536
63.2a
58.1b
-
0-16
16-35
35-53
53+
6.62c
5.58d
7.00b
7.08a
1.45a
1.21b
0.87d
0.89c
1.15a
0.97b
0.87c
0.18d
0.108
0.099
0.094
0.009
1.48a
1.29b
0.23d
0.25c
30
30
25
29
50
43
51
43
20
27
24
27
1.33a
1.21b
-
0.498
0.543
-
56.8a
50.5b
-
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Profile 2
Natural forest
Depth
(cm)
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Land use
type
BD
TP
(g cm-3) (m3 m-3)
EC = Electric conductivity, OM = Organic matter, TN = Total nitrogen, AP = Available phosphorus, BD = Bulk density, TP = Total porosity,
HC = Hydraulic conductivity, WSA = water stable aggregates similar letters are not difference in each soil profiles
Journal of Environmental Biology
September, 2008 WSA
(%)
Effect of modifying land cover and long-term agricultural practises on soil
was significantly reduced > 88% in the natural forest soil to 57% in
cultivated soil (p<0.01). This could be attributed to the breakdown of
aggregates by tillage (Table 2). Duiker et al. (2003) and Celik
(2005) reported that the presence of the aggregates is usually and
positively associated with soil organic matter concentration. Loss of
organic matter is expected to have soil aggregates easily detach
each other and finally the finer particles are transported by water
erosion.
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Fifteen years of continuous cultivation of natural forestland
led to changes in some of the physical, chemical and morphological
properties of soils. Soil characteristics negatively affected by tillage
practices are soil organic matter, total nitrogen, available P content,
total porosity, aggregate stability and bulk density. Especially, after
natural forest land transformation into cultivated land, decreases of
organic matter have crucial effects on soil physical and chemical
properties well explained the vulnerability of the structure and function
of the natural forest system. Therefore, the effect of land use change
on soil physical, chemical and morphological properties should be
accounted for in order to accurately examine and simulate ecosystem
dynamic in the high land mountain ecosystems on the eastern Black
Sea region of Turkey.
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stock of organic matter and nitrogen (p<0.01). This situation may be
related to organic matter mineralization and cultivation practices.
Lobe et al. (2001) and Durak et al. (2006) reported that the organic
matter content in soils decreased rapidly in the first few years they
were cultivated. On the 50-year-old cultivation lands and pasture,
the topsoil contained less organic matter than the continuously natural
forestland due to forest clearance and high decompositions in the
study area. Soil under cultivation and pasture had higher bulk
densities than the adjacent soils under natural forest with an
associated decrease in porosity (p<0.01). It was found that bulk
densities were significantly different between natural forest and other
land uses. This difference can be explained and ascribed to the
compaction of the surface soil due to overgrazing and intensive field
traffic. In addition, loss of organic matter by conversion of the natural
forest into pasture and cultivated lands caused a higher bulk density
in cultivated soils. Similar results were reported by Islam and Weil
(2000) that over the years, continuous tillage practices resulted
bulk density increased from 1.22 to 1.38 g cm-3 in a tropical forest
ecosystem of Bangladesh. Durak et al. (2006) found that the upper
two horizons of soils in cultivated fields were higher than those of the
non-cultivated soils. Use of machines in agricultural operations can
result in increased compaction and bulk density. Messing et al.
(1997) also indicated that the bulk density of soil was lower in soils
under forestland than in soils under field crops. Porosity also
changes due to transformation of natural forestland into pasture and
cultivated lands. While natural forestland has high organic matter
led to low bulk density and increasing total porosity, due to tillage
causing to compaction amount of total porosity diminished under
cultivated lands.
681
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Soil properties modified significantly after natural forestland
transformed into cultivated and pasture lands. In mineral forest soils,
the organic horizons is the layer richest in extractable (plant
available) macronutrients (Urvas and Ervio, 1974). According to
present results, the higher available P content of the soil in 50-yearold cultivated sites found in this study, compared to continuously
natural forestland (p<0.01), is in contrast to the conclusion based on
information in literature reviews that in most cases accumulation of
organic matter which is the source of P. This means that cultivation
has not depleted the P content. This may have resulted from
fertilization of arable land with diammonium phosphate for hazelnut
and corn cultivation. The cultivated soils were considerably lower
in clay than the adjacent soils under natural forest, most likely as a
result of removal of clay by accelerated water erosion. The pH
values of the natural forest, pasture and cultivated lands varied
significantly from 5.09 to 7.34 (Table 2). Natural forest and pasture
soils were more acidic than those of the cultivated sites (p<0.01).
This may be related to agricultural practices such as lime and
physiological basic fertilizer as calcium ammonium nitrate application.
However, soil pH slightly increases with soil depth due to
accumulation of basic cations in cultivated lands. Additionally, similar
results were also determined in EC (p<0.01).
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