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Journal of Chemistry and Chemical Sciences, Vol. 5(4), 145-152, April 2015
(An International Research Journal), www.chemistry-journal.org
ISSN 2229-760X (Print)
ISSN 2319-7625 (Online)
Physico-chemical Characterization of Usar Soil and its
Natural Reclamation by Cyanobacteria
Amrendra Kr. Anand1, Vinod Prasad1 and Mansur Alam2
1
Department of Botany,
B.N. College, Patna, Bihar, INDIA.
2
Department of Chemistry,
B.N. College, Patna, Bihar, INDIA.
(Received on: April 5, 2015)
ABSTRACT
Usar soil is widespread in India and is either saline or alkaline. Such soils
are unproductive, impermeable, hard and compact. Sodic soil limits the plant growth
via poor water infiltration, increased mechanical resistance to root growth, water
logging and poor water availability in the soil profile. The experimentally studied
soil sample have high pH, high exchangeable Na+, K+ and low Ca2+. The low amount
of sulphate and phosphate in usar soil can’t support normal growth of plant species.
These soils also have very low total nitrogen content. All these characteristics make
the usar soil barren. Cyanobacteria act as good fertilizer and they could be used to
reclaim such soil. Heterocystous filamentous forms increase nitrogen content of soil
and are capable of solubilizing microbial nutrients. The mucilaginous sheath of
Cyanobacteria absorbs water and retains it. Comparatively more growth of isolated
Cyanobacteria (Nostoc commune) in usar soil solution than in Allen-Arnon nutrient
medium showed that the strain is alkalophilic and salt tolerant. So, farmers can use
Cyanobacteria to make their agriculture land and usar land nitrogen-rich and fertile
economically and naturally. Usar soil is widespread in India and is either saline or
alkaline. Such soils are unproductive, impermeable, hard and compact. Sodic soil
limits the plant growth via poor water infiltration, increased mechanical resistance to
root growth, water logging and poor water availability in the soil profile. The
experimentally studied soil sample have high pH, high exchangeable Na+, K+ and
low Ca2+. The low amount of sulphate and phosphate in usar soil can’t support
normal growth of plant species. These soils also have very low total nitrogen
content. All these characteristics make the usar soil barren. Cyanobacteria act as
good fertilizer and they could be used to reclaim such soil. Heterocystous
filamentous forms increase nitrogen content of soil and are capable of solubilizing
microbial nutrients. The mucilaginous sheath of Cyanobacteria absorbs water and
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Amrendra Kr. Anand, et al., J. Chem. & Cheml. Sci. Vol.5 (4), 145-152 (2015)
retains it. Comparatively more growth of isolated Cyanobacteria (Nostoc commune)
in usar soil solution than in Allen-Arnon nutrient medium showed that the strain is
alkalophilic and salt tolerant. So, farmers can use Cyanobacteria to make their
agriculture land and usar land nitrogen-rich and fertile economically and naturally
Keywords: Usar soil, Sodicity, Reclamation, Cyanobacteria.
1. INTRODUCTION
Usar soils are unproductive, impermeable and hard due to the presence of
undesirable salts on the surface. These soils are grouped into two broad categories- the
saline (solenchak) and the alkaline (solonetz or Sodic). Sodic soils are characterized by high
exchangeable Na+ ions (more than 15%), low quantities of Ca²+, and high pH values that
usually range between 8.5 and 10.512. Alkaline soils have poor hydraulic conductivity and
reduced aeration4. Salt affected soils occur both naturally and as the result of man’s
modification of the hydrologic processes, which mobilize and accumulate salts within the
landscape. Saline soils are those having elevated concentration of any kind of salt, whereas
Sodic soils have a high proportion of sodium ions relative to other cations in the soil9. Sodic
soils have high concentrations of free carbonate and bicarbonate and excess of sodium on the
exchangeable site of clay particles. They are deficient in Nitrogen, Phosphorous and Zinc.
Clay fraction and organic matter are dispersed, thus such soils are sticky when wet and hard
when dry. There is very poor hydraulic conductivity and high impedance to root growth.
Nearness of water table and impedance in the downward movement of water due to the
presence of an indurated layer in the lower depth (in rooting zone of plants) seems to be the
chief cause of increase in salinity12. According to Voelcker (1898)13, the origin of injurious
alkali salt due to weathering of igneous rocks is the main cause of sodicity.
1.1 Effect of sodicity and salinity on soil physical properties
Too much increase in salt concentration (usually NaCl) in the soil causes both
sodicity and salinity. But sodicity and salinity are responsible for different problems for
plants. In sodic soil, sodium is attached to the clay. A soil is considered sodic when the
sodium reaches a concentration, where it starts to affect the soil structure. Sodium weakens
the bond between soil particles when wetted, resulting in the clay swelling and often
becoming detached. This causes spreading of clay particles and making the soil water cloudy
(called as dispersion). The dispersed clay particles can then move through the soil clogging
pores. Both swelling and dispersion reduces infiltration and drainage. Once the sodic soil is
broken down into very fine particles, it can easily be moved by water or wind11. In saline
soil, sodium is found in the form of soluble salts (mainly NaCl), which can be easily
dissolved and moved in soil water. Soluble salts reduce the availability of water to the plants
by decreasing water potential of the soil water. High sodicity causes clay to swell excessively
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147
when wet. The clay particles move so far apart that they separate (disperse). This weakens
the aggregates in the soil, causing structural collapse and closing-off of soil pores. For this
reason water and air movement through sodic soils is severely restricted. In vegetable crops,
sodic layers or horizons in the soil may prevent adequate water penetration during irrigation,
making the water storage low. Additionally, water logging is common in sodic soil, since
swelling and dispersion closes off pores, reducing the internal drainage of the soil. Sodicity
of the surface soil is likely to cause dispersion of surface aggregates, resulting in surface
crusts.
Table 1: Profile characteristic of Usar soil
Horizons
A
Depth in inch
0-11
B
11-24
24-38
C
38-72
Morphology
Dark gray in colour; clayey loam in texture; cloddy structure;
alkaline in reaction; very slightly calcareous; hard and compact.
Ash gray in colour; clayey in texture; cloddy structure; alkaline
in reaction; calcareous; ‘Kankar’ nodules present; harder than
above.
Ash gray in colour with yellow tinge; clayey in texture; cloddy
in structure; alkaline in reaction ; strongly calcareous ; hard pan
of ‘Kankar’ present.
1.2 Transformation of saline soil into sodic soil
A saline soil becomes sodic through the leaching of salt (eg. NaCl). As salt is
washed down through the soil it leaves some sodium behind bound to clay particles
displacing more useful substances such as calcium. This sodium builds up in the soil and
interferes with soil structure11.The amount of sodium and salt left determines whether the soil
is non-sodic (very little sodium), sodic (a lot of sodium), or saline and Sodic (a lot of salt and
sodium). In such soils, a hard impervious pan consisting of indurated clay and often
embedded with small ‘ kanker’ nodules exists , which does not allow any connection for the
circulation of moisture between the surface and the bottom layer, both of which may be quite
pervious. This virtually stops moisture contact between the top and the bottom of the soil
profile and downward percolation of water is altogether stopped, resulting in increase of
salinity in the root zone12.
1.3 Reclamation of Sodic Soil by displacement process
Reclamation or improvement of Sodic soils requires the removal of part or most of the
exchangeable sodium ion and its replacement by the more favourable calcium ions in the root
zone11. Soil amendment materials such as gypsum or calcium chloride directly supply soluble
calcium for the replacement of exchangeable sodium, or other substances, such as sulphuric
acid and sulphur that indirectly through chemical or biological action, make the relatively
insoluble calcium carbonate commonly found in sodic soils, available for replacement of
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Amrendra Kr. Anand, et al., J. Chem. & Cheml. Sci. Vol.5 (4), 145-152 (2015)
sodium. The application of mined-gypsum in soils and addition of sulphuric acid to sodic soil
surface reduce soil crusting and improve water infiltration rate2. Organic matter (straw, farm
and green manures), decomposition and plant root action also help to dissolve the calcium
compounds found in most soils, thus promoting reclamation but this is relatively a slow
process.
Fig.-1
1.4 Cyanobacteria: A potential agent for reclamation of Sodic soil
Sodic soil has high pH and high exchangeable Na+-ion and is often barren.
Cyanobacteria however tolerate excess Na and grow extensively on the soil surface in wet
season. Cyanobacteria tolerant to sodicity accumulate inorganic ions, organic compounds
(sugar, polyols, quaternary amines etc.) and osmoregulators10. The enrichment of such soils
with native cyanobacteria, over a period of time improved the soil quality6 and making it
arable by bringing about a decrease in pH , exchangeable sodium, Na/Ca and overall increase
in Nitrogen and Phosphorous, organic matter and water holding capacity of soil. This
ultimately lowers the sodium adsorption ratio, which is an index of alkalinity and improve
the hydraulic conductivity of sodic soils. Cyanobacteria, a group of Gram negative bacteria,
play significant role in reclamation of such unproductive usar soils. Cyanobacteria form a
thick stratum on the surface of soil during the rainy season and the winter month1. The algal
material incorporated in the soil conserve organic C, organic N, and organic P as well as
moisture, and converts Na+ to Ca2+. Organic matter and Nitrogen added by cyanobacteria
bind the soil particles, and thus improve soil permeability and aeration12. They are capable of
solubilizing microbial nutrients and dissolving insoluble carbonate nodules through the
secretion of oxalic acid12. Cyanobacteria improve the soil aggregation by lowering the pH
and electrical conductivity & increasing the hydraulic conductivity of saline and alkali soil8.
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2. MATERIAL AND METHODS
2.1 Site description and collection of soil sample
Soil samples were collected from Amra Khera village, Chhitaipur, Suswahi road,
Varanasi, which is located approx. 6.0 km south from Banaras Hindu University (BHU)
campus. Soil was collected in polythene bags.
2.2. Experiments
Soil solution was prepared by dissolving soil in double distilled water and filtered to
measure the pH. The total nitrogen of the samples was estimated by Micro-Kjeldahl Method7
by using total nitrogen auto-analyzer. The total phosphorus was estimated by Ascorbic acid
Method5. The amount of sulphate estimated turbidometrically by taking absorbance in the
spectrophotometer. For estimating Na+, K+, and Ca2+, soil samples were prepared by
digesting them in acid mixture (HNO3: HClO4:: 10:1)8. All the measurements were carried
out in triplicate.
Cyanobacterial strains were isolated and purified in aseptic laboratory condition.
The purified strains are identified with the help of the text ‘Cyanophyta’ written by T.V.
Desikachary3. The identified cyanobacterial strains were cultured in both Allen –Arnon
Medium1 without nitrate and differentially diluted usar soil solution in optimal growth
condition of light and dark period (16:08 hr.) at temperature (28±1⁰C). Growth behavior of
cyanobacteria measured turbidometrically with the help of spectrophotometer by taking
absorbance at 650 nm every day and plotted graph of day vs absorbance.
3. RESULTS AND DISCUSSION
The inability of user soil in providing various nutrients for biological production are
assessed through the analysis of important constituents such as pH, total alkalinity, nitratenitrogen, phosphate- phosphorous, sulphate-sulphur, sodium, potassium and calcium. The
observed value of these parameters are given in the table-1 based on quantative analysis.
Table-1:- Results of quantitative analysis of user soils
SI.No.
1.
2.
3.
4.
5.
6.
7.
Parameters
pH
N%
Phosphate
Sulphate
Sodium-mg/it.
Potassium-mg/lit.
Calsium
Observed value of user soil
10.17
0.168µM
6.25
10.54ppm
103.56
77.03
8.73ppm
All the saline and alkaline soils are placed under the category of Usar soil and are
widespread in India. The saline soil having high percentage of NaCl are called ‘’Sodic
Soils’’. It inhibits the growth of sensitive plants as it has poor water infiltration, increased
mechanical resistance to root, water logging and poor water availability in the soil profile.
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Amrendra Kr. Anand, et al., J. Chem. & Cheml. Sci. Vol.5 (4), 145-152 (2015)
3.1 Growth of Nostoc commune in differently diluted Usar soil solution
(a)
(b)
( c)
(d)
Fig.-2: (a) and (b) show akinet germination.while (c) and (d) show filament heterocysts.
3.2 Growth behavior of Nostoc commune in different diluted usar soil solution and
Allen-Amon mrdium
Fig.-3
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151
The pH of the soil sample was found highly alkaline (pH =10.17). The pH value
coincide with soil quality standard15. Soil pH in the range of 6.5 to 7.5 is considered ideal.
Sodium is required by all plants up to a certain limit. If it’s concentration increases beyond a
threshold level, it poses threat to plants. Below the threshold level, Sodium is required by the
plants for Nitrogen-metabolism in the synthesis of amino acids, proteins and also for
transport of sugar.
In the Usar soil amount of sulphate is very less (10.54ppm) as compare to the normal
fertile soil (710ppm). And also total nitrogen content of such soil is very low (0.168%) which
does not support normal growth of plants. Nitrogen deficiency causes chlorosis, dormancy of
lateral buds, wrinkling of cereal grains. Nitrogen is also one of the major constituent of
proteins, nucleic acids, vitamins and hormones.
Phosphorus content of Usar soil is also very low (6.25µM) while it is an important
constituent of cell membrane, proteins and nucleic acids. So its deficiency causes delayed
seed germination, leaf spotting and premature leaf fall.
The amount of Ca2+ content of Usar soil is very low (8.3ppm). Calcium is needed for
cell division, differentiation, synthesis of cell wall and middle lamella. So,deficiency of Ca2+
causes stunted growth of plant.
Culture of Nostoc. commune in soil solution (w/v, 1:1) shows comparatively slow
growth with comparison to that of 1:2, 1:3 and 1:4 times diluted. And growth rate was
slowest in Allen-Arnon-Medium (pH 7.5). This signifies that the Nostoc. commune is
alkalophilic and salt tolerant.
4. CONCLUSION
The present study about usar soil reveals that invasion of cyanobacteria in such soil
promotes soil genesis, add humus, dissolves certain minerals, increases moisture content (1015%), increase polysaccharide content, reduce soil loss and improve texture. The
mucilaginous sheath of the cyanobacteria is able to absorb and retain water1. They increase
soil nitrogen content by Nitrogen fixation.In this way, cyanobacteria promotes soil genesis
and act as a good bio-fertilizer and gradually the bacterium converts Usar soil into a fertile
soil.
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