Effect of Soil Moisture Regime and Rice Cultivation on Mineralogical Characteristics of Paddy Soils of Mazandaran Province, Northern Iran, Amol
The clay mineralogy of paddy soils with different water
table depth and drainage of Northern Iran were investigated to determine
their origin and factors controlling their distribution pattern in soils.
In this study sand, silt and clay fractions were separated by centrifuge
after the removal of organic matter, carbonates and sesquioxides. For
identification of clay minerals, clay suspensions were saturated by Mg
and K and then 10 mg of clays were placed on glass slides for XRD analysis.
In all of the soils studied, smectite, illite, chlorite, kaolinite and
quartz were identified. Clay mineralogy is probably more affected by parent
materials and less influenced by aquic and anthraquic conditions. However,
there are some indications that aquic and anthraquic condition may affect
on quantity of clay minerals, as shown by higher smectite in poorly drained
Clay is the result of the aqueous solutions interaction with rocks. The
dissolution and decrystalization is the process by which they are formed
and transformed (Velde, 1995). Mineral compositions of the paddy soil
with permanent reduce condition in Gilan Provinces, Northern Iran were
investigated by Gelsefidi et al. (2001). In all of the soil studied
smectite, illite and chlorite were identified. Khormali and Abtahi (2003)
suggested smectite formation in poorly drained soil with low water table
depth of soils. Therefore, the main objectives of this study (1) Semi-quantitative
and qualitative determination, the origin and distribution patterns, (2)
effect of aquic and anthraquic condition on clay minerals.
MATERIALS AND METHODS
The study area (at the East of Amol city) is located in Mazandaran
Province, Northern Iran, in the southern coast of the Caspian Sea (Fig.
1), with different water table depth (Fig. 2). Studied
area has general slope from south to east. Its physiographic unit is alluvium
plain. A humid climate with moderate temperature characterizes the area.
The mean annual temperature is approximately 16.0Â°C. This area has
an average annual rainfall of 848.4 mm (1988-1998). The soil moisture
and temperature regimes are Wet Ustic and Thermic, respectively. The parent
materials are derived from sediments weathered from primary rocks content
Calcite, Dolomite and loess moved to this plain.
This study was accomplished from September 2005 to September 2006.
Seven pedons (35 paddy soil samples) and 1 pedon (4 soil samples) as a
blank (soil under cultivation of citrus fruit) were selected. Soil samples
described and classified, according to keys to soil taxonomy (Soil Survey
Staff, 2006). Four representative pedons (16 samples) were considered
for further mineralogical study.
|| The location of Mazandaran Province and Amol area
|| The location of pedons according to water table depth
Air-dried soil samples were crushed and passed through a 2 mm sieve.
Samples were dispersed using sodium hexametaphosphate for determination
of sand, silt and clay fraction by the hydrometric method (Bouyoucos,
1962). Organic matter was measured by wet oxidation (Nelson and Sommers,
1982). Alkaline-earth carbonate (lime) was measured by acid neutralization
(Ehyaee and Behbahanizade, 1993). Soil pH was determined with a glass
electrode in saturated paste (Ritvo et al., 2003). Electrical conductivity
(total soluble salt) was measured in the saturation extract (Ehyaee and
Behbahanizade, 1993). Cation Exchange Capacity (CEC) was determined using
sodium acetate (NaOAc) at a pH of 2.8 (Bower and Hatchea, 1966).
Removal of chemical cementing agents and separation of clay fractions
was carried out according to Kittrick and Hope (1963) and Jackson (1975).
The carbonates were removed using 1 N sodium acetate buffered at pH =
5. The addition of 1 N sodium acetate was continued until no effervescence
was observed with 1 N HCl (Jackson, 1975). The reaction was performed
in a water bath at 80Â°C. Organic matter was oxidized by treating the
carbonate-free soils with 30% H2O2 and digestion
in a water bath. Iron oxides were removed from the samples by the dithionate
citrate bicarbonate method. The iron oxide-free samples were centrifuged
and clay separates were removed. Additionally, for removal of the fine
clay (particles <2/0 Î¼m), clay separates were centrifuged according
to Kittrick and Hope (1963). The (001) reflections were obtain following
Mg saturation, ethylene glycol salvation and K saturation. The K saturated
samples were studied after drying and heating at 550Â°C for 4 h. A
total number of 16 clay samples from soils and parent rocks were studied
RESULTS AND DISCUSSION
Soil profile description and some physical and chemical properties are
shown in Table 1. In studied area pedon 5 is located
Northern and lowland part of this region. The water table was at (or close
to) the surface through out the year. Only some years in harvesting time
and 2-3 weeks after harvesting is not flooded, but the soil surface is
mostly wet because of arrival deposition from top land. Soil development
of this pedon is the last, which has undergone little soil formation.
The other pedons were not saturated all of the year and the water table
fluctuation was influenced by cropping and flooding of the rice-growing
and rainfall. Pedon 7 and 8 were at southern of studied area that have
the height water table depth and locate in top land. Pedons 1, 2, 3 and
4 were located between pedons 5 and 7. Rice soils are mostly found in
the alluvial lowland in humid regions. This implies that in the genesis
of rice soils the soil material factor is one primary importance. Several
processes may account for formation variety soils in this region, such
as physical properties of parent material, organic matter repletion, clay
mineral formation and their translocation by flooding and cropping and
oxidation and reduction processes. The parent material of this area is
mainly from lime and most of the soils are calcareous throughout. The
electrical conductivities (EC) of all soil are less than 4 ds m-1.
Organic matter content in all surface horizons are more than 1%, especially
pedon 5. This increasing maybe related to weak oxidation and low activity
of microorganisms because of flooding and reduces condition. The pH range
in the studied pedons is 7-8. The CEC of the soils which is dependent
on the amount and the type of clay minerals, ranges from 10-40 cmol(+)
kg-1 (Table 1).
|| Relative abundance of clay minerals of studied soils
and parent rock
|+: 0-10, ++: 10-20, +++: 20-30, ++++: 30-40, +++++:
>40, ND: No Define
Clay Mineralogy of Soils
The semi-quantitative analysis of clay minerals and XRD patterns of
clay in the studied area are shown in Table 2 and Fig.
3-6. Smectite, illite, chlorite and kaolinite are
the major clay minerals of both paddy soils and the blank pedon. Studies
by XRD revealed that illite is a commonly observed clay mineral in well
drained pedons, which their abundance in soils is largely due to their
presence in parent rock.
|| XRD patterns of clay in parent rock (A) and in APg
horizon (B) of pedon 1, respectively
|| XRD patterns of clay in APg horizon (A)
and in parent rock (B) of pedon 5, respectively
|| XRD patterns of clay in parent rock (A) and in Bw1
horizon (B) of pedon 7, respectively
|| XRD patterns of clay in parent rock (A) and in Bg1
horizon (B) of pedon 8, respectively
It is formed in pedogenic and sedimentary environment and also is
commonly believed to be inherited largely from parent rock. Wilson (1999),
Bronger et al. (1998) and Sanguesa et al. (2000) had the
same result from their study too. A few studies have documented illite
formation in soil by weathering of feldspars, increasing of soil leaching
make a condition that K release from mica and are weathered and transform
to 2:1 clay minerals (Dixon and Weed, 1989; Nanzyo et al., 1999;
Lee et al., 2003; Kitagawa and Itami, 1996). One of the primary
reasons for decreasing illite in surface is simple transformation to the
other clay minerals especially smectite, because of the relative leaching
environment for the release of K from micaceous minerals and mainly illite.
The alteration of this mineral is due to the decrease of iron content,
the decrease of layer charge and the degradation of crystal structure,
through the pedogenesis under the seasonally reductive condition.
It is the main clay mineral in surface and near surface and near surface
reduced horizons of weakly drained pedons. The presence of large amounts
of this mineral in poorly drained pedons with low water table depth is
reported by Abtahi and Khormali (2001) and Aoudjit et al. (1995).
They discussed there are 3 main sources of smectite in soils: (1) neoformation
from soil solution, (2) detritial origin or inheritance, (3) transformation
of other clay minerals. Low-lying topography, poor drainage and base-rich
parent material, favorable chemical conditions characterized by high pH,
high silica activity and an abundance of basic cations are the factors
strongly influenced the origin and distribution of smectite in soils.
Neoformation of Smectite was also reported, but illite transformation
to smectite is a major source of this mineral in studied soil. When illite
is exposed to weathering, K exit from illite layers and this condition
is suitable to form smectite. Many researcher reported illite transformation
to smectite as a main source of this mineral. Khormali and Abtahi (2003)
found smectite in soils with poorly-drainage soils relate to well drained
soils, like in pedon 5 with this condition we have high percent smectite,
but in pedons 1, 7 and 8 smectite decreases with depth, because of high
water table depth, well drained condition and also high leaching of basic
cations, made unstable environment for smectite forming chemically. In
pedon 5 with anthraquic condition, high enough base cation content can
effects on pedogenic forming of this clay mineral.
It is also an inheritance clay mineral in the studied area as well
as illite, but it does not show any regular pattern with increasing depth
(Table 2). The dehydroxilation and oxidation of Fe+2
cause chlorite to transform to the other clay minerals. One of the important
reasons of chlorite stability in reduced studied soil is consistency of
Fe+2 exist in this clay mineral. In developed weathering, chlorite
transform to kaolinite and free Fe oxides.
It is not seen in studied soil samples. Vermiculite role as a halfway
product, forming from mica (Nanzyo et al., 1999; Lee et al.,
2003) and transform to smectite in poor drained condition. The same is
reported by Kittrick and Hope (1963) too.
Soil mineralogy is one of the most important determinants of the inherent
capability of rice soils considered on a regional scale, differentiation
of soil quality according to mineralogy is relatively clear when rice
is grown with little or no added plant nutrition, or at a low level of
management and also, clay minerals recognition, have important implications
for agricultural and environmental purposes because of adsorption, fixation
and release of nutrition elements in clay part. Clay mineralogy is probably
more affected by parent materials and less influenced by aquic and anthraquic
condition, in most cases the materials deposited as alluvial sediments
have been barely altered by the natural and artificial processes inherent
in rice cultivation. Accordingly, the mineralogy of rice soils is almost
the same as that of their parent materials. However, there are some indications
that aquic and anthraquic condition may affect on quantity of clay minerals,
as shown by higher smectite in poorly drained soils. There are two factors
to consider in evaluating the mineral composition of rice soils; one factor
is that rice soils in this area occur in alluvial lowlands and their parent
materials have been sorted by the sedimentation process. In low land sediments
are brought in by floodwater from rivers and by irrigation. The improving
action of the floodwater sediments depends, of course, on the source of
the floodwater. The other factor is that the rice soils are distributed
in more or less humid, warm to hot regions, that implies that soil materials
had generally been strongly weathered and leached even before rice cultivation
started. These two factors would suggest generally low importance of sand-size
grains in paddy soils as the source of plant nutrients, in terms of both
quantity and quality.
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