Soil PH Soil
Acid Soils Alkaline
Soils Soil Testing
Of Soils In Andhra Pradesh
Classification Of Soils In India
Definiton of Soil
- It refers to the arrangement of soil particles.
It is one of the important property of soil, since it influences aeration,
permeability and water capacity.
Types of structure
- Platy - Horizontal alignment
- Prism like - Columnar type
- Block like - Angular or
sub- angular types
- Spiroidal - Granular and crumb types
- The varying proportions of particles of different
size groups in a soil constitute is known as soil texture.
- The principle textural classes are clay, clay loam,
sandy clay, silt clay, sandy clay loam, silty clay loam, sandy loam,
silt loam, sand, loamy sand and silt.
- It is the vertical section of the soil through all
its horizons from the surface to the unaffected parent materials''.
Generally the profile consists of three mineral horizons viz., A,
B and C.
- The surface soil or that
layer of soil at the top which is liable to leaching and from which
some soil constituents have been removed is known as horizon 'A' or
the horizon of eluviation. The intermediate layer in which the materials
leached from horizon 'A' have been re-deposited is known as horizon
'B' or the horizon of illuviation. The parent material from which
the soil is formed is known as horizon ' C'.
- The soil in each of these
horizons is usually uniformly developed and presents a more or less
homogeneous character. Each layer or horizon develops specific morphological
features such as the size and shape of particles, their arrangement,
colour, consistence etc. which distinguish from one horizon to another.
- Study of soil profile is important since it reveals
the characteristics and qualities of the soil.
- Organic matter
- Soil organisms - Micro flora and Micro fauna.
- Soil water
- Soil air
- Inorganic matter - Macro nutrients and Micro
- The plants and animals grown in weathered material
and the organic residues left behind decay with time and become an
integral part of the soil. The main source of soil organic matter
is plant tissue. Animals are subsidiary source of soil organic matter.
- The micro flora like bacteria, fungi, algae, actinomycetes,
and micro fauna like protozoa, nematodes, macro fauna like earthworms,
ants etc. play an important role in formation of organic matter.
- The organic matter influences the soil in respect
to colour, physical properties, supply of available nutrients and
- Soil is the habitat for enormous number of living
organisms. Some of these organisms are visible to naked eye where
as others can be seen by microscope only.
- Roots of higher plants are considered as soil
macro flora while bacteria, fungi, algae and actinomycetes are considered
as soil micro flora. Protozoa and nematodes are the significant soil
micro fauna where as the earthworms, moles and ants constitutes soil
- In order to function as a medium for plant growth,
soil must contain some water. The main functions of water in the soil
are as follows:
- Promotes many physical and biological activities
- Acts as a solvent and carrier of nutrients.
- As a nutrient itself.
- Acts as an agent in photosynthesis process.
- Maintains turgidity of plants.
- Acts as an agent in weathering of rocks and minerals.
- Oxygen is essential for all biological reactions
occurring in soil. Its requirement is met from the soil air.
- The gaseous phase of soil acts as a path way for
intake of oxygen which is absorbed by soil micro organisms, plant
roots and for escape of carbondioxide produced by the plants.
- This two way process is called soil aeration. Soil
aeration become critical for the plant growth when water content is
high, because water replaces soil air.
Soil Inorganic Matter
- The inorganic constituents of the soil comprises
carbonates, soluble salts, free oxides of iron, aluminium and silica
in addition to some amorphous silicates.
- The inorganic constituents forms the bulk of the
solid phase of the soil. Soils having more than 20% of the organic
constituents are designated as organic soils.
- Soils where inorganic constituents dominates they
are called mineral soils. The majority of the soils in India are mineral
- The negative logarithm of hydrogen ion ( H +) concentration
is called pH. Soil pH may be acidic, basic or neutral.
- Soil fertility deals with the nutrient status or
ability of soil to supply nutrients for plant growth under favourable
environmental conditions such as light, temperature and physical conditions
- Soil productivity is defined as the capability
of the soil for producing a specified quantity of plant produce per
unit area and the ability to produce sequence of crops under a specified
system of management.
- The soils which owe characteristics that they
can not be economically used for the cultivation of crops without
adopting proper reclamation measures are known as problem soils.
- Those soils with pH less than 6.5 and which
respond to liming may be considered as acid soils.
Reasons for Acidity
- Humus decomposition results in release of large amounts
of acids. There by lowering the pH.
- Rainfall : In areas with more than 100 cm rainfall
associated with high R.H., Ca, Mg is dissolved in water and leached
out due to this base saturation of soil decreases.
- Application of elemental sulphur under goes reactions
resulting in formation of H2So4.
- Continuous application of acid forming fertilizers
like ammonium sulphates or ammonium chlorides results in depletion
of Ca by CEC ( cation exchange capacity) phenomenon.
- Parent Material : Generally rocks are considered
as acidic, which contain large amount of silica (Si o2) when this
combined with water, acidity increases.
- PH is less than 6.5
- This soils are open textured with high massive Structure.
- Low in Ca, Mg with negligible amount of soluble salts.
- This soils appear as brown or reddish brown,
sandy loams or sands.
Injury to Crops
- Plant root system does not grow normally due to toxic
- Permeability of plant membranes are adversely affected
due to soil acidity.
- Enzyme actions may be altered, since they are
sensitive to PH changes.
- Deficiency of Ca and Mg occur by leaching.
- Al, Mn and Fe available in toxic amounts.
- All the micro nutrients except molybdenum are
available. So 'Mo' deficiency has been identified in leguminous crops.
- Phosphorous gets immobilized and its availability
Actvity of Micro Organisms
- Most of the activities of beneficial organisms
like Azatobacter and nodule forming bacteria of legumes are adversely
effected as acidity increases.
Crops Suitable For Cultivation in Acid Soil
|Citrus, Blue berries
Tobacco, Apple, Grapes, Plum, watermelon
|Cowpea, Soybean, Cotton, Wheat, Oat,
Peas, Tomato, Sorghum.
|Peanut, Cabbage, Carrot, Onion,
Radish, Spinach, Cauliflower.
- Lime as reclaiming agent : Lime is added to
neutralize acidity and to increase the PH, so that the availability
of nutrients will be increased.
- Basic slag obtained from Iron and steel industry
can be substituted for lime. It contains about 48-54% of CaO and 3-4%
- Ammonium sulphate and Ammonium chloride should
not be applied to acid soils but urea can be applied.
- Calcium Ammonium Nitrate (CAN) is suitable
to acid soils.
- Any citrate soluble phosphate fertilizer is
good source of phosphorous for acid soils.
- Eg. Dicalcium phosphate (DCP), Tricalcium phosphate
- Potassium sulphate is a suitable source of
'K' for acid soils. But MOP is better than K2So4 because Cl of MOP
replaces -OH ions, their by release of -OH ions tends to increase
- Alkali soils are formed due to concentration
of exchangeable sodium and high pH. Because of high alkalinity resulting
from sodium carbonate the surface soil is discoloured to black; hence
the term black alkali is used.
Reasons for Alkalinity
- The excessive irrigation of uplands containing Na
salts results in the accumulation of salts in the valleys.
- In arid and semi arid areas salt formed during weathering
are not fully leached.
- In coastal areas if the soil contains carbonates
the ingression of sea water leads to the formation of alkali soils
due to formation of sodium carbonates.
- Irrigated soils with poor drainage.
Injury to Crops
- High exchangeable sodium
decreases the availability of calcium, magnesium to plants.
- Dispersion of soil particles
due to high exchangeable 'Na' leads to poor physical condition of
soil, low permeability to water and air, tends to be sticky when wet
and becomes hard on drying.
- Toxicity due to excess hydroxyl
and carbonate ions.
- Growth of plant gets affected
mainly due to nutritional imbalance.
- Restricted root system and
delay in flowering in sensitive varieties.
- Typical leaf burn in annuals
and woody plants due to excess of chloride and sodium.
- Bronzing of leaves in citrus.
- It effects the solubility of zinc( Zn).
Crops Suitable for Cultivation
in Alkaline Soils
- Barley, Sugarbeet, Cotton, Sugarcane, Mustard, Rice,
Maize, Redgram, Greengram, Sunflower, Linseed, Sesame, Bajra, Sorghum,
Tomato, Cabbage, Cauliflower, Cucumber, Pumpkin, Bitterguard. Beetroot,
Guava, Asparagus, Banana, Spinach, Coconut, Grape, Datepalm, Pomegranate.
- The process of amelioration consists of two
- To convert exchangeable sodium into water soluble
- To leach out the soluble sodium from the field.
Amendments used for reclamation of Alkali soils.
- It is slightly soluble in water. So it should
be applied well in advance.
- For every 1 m.e of exchangeable Na per 100
gm of soil, 1.7 tonns of Gypsum/ acre is to be added.
- If the requirement is 3 tonnes/ acre- apply in one
- If the requirement is 3 to 5 tonnes/acre- apply in
2 split doses.
- If the requirement is 5 or more tonnes/ acre - apply
in 3 split doses.
- Use of Pyrites (Fe S2)
- Sulphur present in pyrites causes decrease in pH
of soil due to formation of H2So4.
- H2So4 + Ca Co3 -- Ca S04 Ca So4 + Na --- Na So4 +
Ca ( leachable)
- Application of sulphur.
- Application of molasses.
- Drainage channels must be arranged around the field.
- Growing the green manure crops and incorporate in
||more than 8.3
||More than 15
|Chemistry of soil solution
||Dominated by carbonate and bicarbonate
ions and high exchangeable sodium.
|Effect of electrolyte on soil particles
||Dispersion due to high amount of exchangeable
|Adverse effect on Plant
||Alkalinity of soil solution
||Semi arid and semi humid - areas.
|Diagnosis under field condition
||Presence of dispersed soil surface. Columnar
structures present in the sub-soil
- The saline soils contains toxic concentration
of soluble salts in the root zone. Soluble salts consists of chlorides
and sulphates of sodium, calcium, magnesium. Because of the white encrustation
formed due to salts, the saline soils are also called white alkali soils.
Reasons For Salinity
- In arid and semi arid areas salts formed during weathering
are not fully leached. During the periods of higher rainfall the soluble
salts are leached from the more permeable high laying areas to low laying
areas and where ever the drainage is restricted, salts accumulate on
the soil surface, as water evaporates
- The excessive irrigation of uplands containing salts
results in the accumulation of salts in the valleys.
- In areas having salt layer at lower depths in the profile,
seasonal irrigation may favour the upward movement of salts.
- Salinity is also caused if the soils are irrigated
with saline water.
- In coastal areas the ingress of sea water induces salinity
in the soil.
||Less than 8.3
||More than 4.0 m.mhos/ cm
|ESP (exchangeable sodium %)
||Less than 15
|Chemistry of soil solution
||Dominated by sulphate and chloride ions
and low in exchangeable sodium
|Effect of electrolytes on soil particles
||Flocculation due to excess soluble salts.
|Main effect on plant
||High osmotic pressure of soil solution
||Arid and semi arid regions.
|Diagnosis under field condition
Presence of white crust
Presence of chloris barborata(weed)
Patchy growth of plants.
Injury to Crops
- High osmotic pressure decreases the water availability
to plants hence retardation of growth rate.
- As a result of retarded growth rate, leaves and
stems of affected plants are stunted.
- Development of thicker layer of surface wax imparts
bluish green tinge on leaves
- Due to high EC germination % of seeds is reduced.
Crops Suitable For Cultivation In Saline Soils
- Barley, Sugarbeet, Cotton, Sugarcane, Mustard,
Rice, Maize, Redgram, Greengram, Sunflower, Linseed, Sesame, Bajra,
Sorghum, Tomato, Cabbage, Cauliflower, Cucumber, Pumpkin, Bitterguard.
Beetroot, Guava, Asparagus, Banana, Spinach, Coconut, Grape, Datepalm,
- The salts are to be leached below the root zone and
not allowed to come up. However this practice is some what difficult
in deep and fine textured soils containing more salts in the lower layers.Under
this conditions a provision of some kind of sub-surface drains becomes
- The required area is to be made into smaller plots
and each plot should be bounded to hold irrigation water.
- Separate irrigation and drainage channels are to be
provided for each plot.
- Plots are to be flooded with good quality water upto
15 - 20 cms and puddled. Thus, soluble salts will be dissolved in the
- The excess water with dissolved salts is to be removed
into the drainage channels.
- Flooding and drainage are to be repeated 5 or 6 times
till the soluble salts are leached from the soil to a safer limit.
- Green manure crops like Daincha can be grown upto flowering
stage and incorporated into the soil. Paddy straw can also be used.
- Super phosphate, Ammonium sulphate or Urea can be applied
in the last puddle. MOP and Ammonium chlorides should not be used.
- Scrape the salt layer on the surface of the soil with
- Grow salt tolerant crops like sugar beet, tomato, beet
root, barley etc
- Before sowing , the seeds are to be treated by soaking
the seeds in 0.1% salt solution for 2 to 3 hours.
- Need : When land is brought under cropping, grain
or fruit and sometimes the entire plants are removed (harvested) from
the land. Hence, the soil losses a considerable amount of its nutrients
(up take by plants). If cropping is continued over a period of time,
without nutrients being restored to the soil, its fertility will be
reduced and crop yields will decline.
- Apart from removal by crops, nutrients may also
be lost from the soil through leaching and erosion. Even to maintain
soil productivity at the existing levels, it is necessary to restore
to the soil, the nutrients removed by crops as also those lost through
leaching and erosion.
- Continued maintenance of a high level of soil
fertility is an indispensable for profitable land use and sustained
agricultural production. From time to time the inherent fertility of
soil has to be evaluated.There are different methods for soil fertility
evaluation as listed below:
Visual method of diagnosis
- Plant analysis (Analysis of whole or part of plant
growing on the soil in question).
- Biological tests in which higher plants or certain
micro organisms are used.
- Soil tests.
- Field experiments.
- Among the different methods, soil testing is a better
method for the following reasons.
- Soil testing, being a rapid method, is an advantage
over the biological methods which are relatively elaborate and time
consuming. It is also better than deficiency symptoms and plant and
tissue analysis, because the needs can be determined before the crop
is planted while in the other methods the crop needs can be ascertained
only after the crop is grown, by which time it may be late to correct
any nutritional deficiencies that may be indicated.
- The main purpose of soil testing is to evaluate the
fertility status of the soil. It provides a basis for fertilizer, lime
and gypsum recommendation. Laboratory test is a means of making an inventory
of the chemical conditions of soil and determining treatments, if any,
are needed. Soil test information is then used along with an evaluation
of specific crop requirements, cropping history and physical characteristics
of the soil for determining the exact amounts of different nutrients
and soil amendments, if any, needed for a certain crop or cropping sequence.
With this objective in view, a number of soil testing laboratories have
been established in the country by the State Governments, Agricultural
Universities and fertilizer industry for making fertilizer recommendations
to farmers on the basis of the fertility status of their soils. This
service is generally rendered free of cost.
- Based on analysis, soils are classified into
three categories i.e., low, medium and high, in respect of their available
content of each nutrient according to the ratings of soil reaction.
Soil Test Interpretation and Fertilizer Recommendations
- From the results of analysis of soil samples sent by
the farmer and information sheet supplied by him, soil test reports
are prepared in the laboratories. Copies of these reports are sent to
the concerned farmer.
- Soil test reports are usually in three main parts.
First part indicates results of analyses of the soil sample. Most laboratories
give actual analyses as well as the ratings. Second part is fertilizer
recommendations for the crop based on soil analyses, history of the
field like cropping pattern, manures and fertilizers earlier applied,
etc. This part indicates quantities of nitrogen (N), Phosphate ( P205),
Potash(K20), Zinc (Where facilities exist ) and also of lime or gypsum
to be applied per hectare. Most laboratories also show in the report
optimum quantities of organic manures as per recommendations of the
- The third part of the report usually indicates time
and methods of fertilizer application and other practices required to
make the fertilizer use more efficient.
- During the relatively short period that soil
testing service has been in operation in this country a large number
of soil samples have been analyzed in various laboratories. Based on
the results of these analyses , soil fertility maps have been prepared
indicating the nutrient status of nitrogen, phosphorus, potassium and
zinc in different parts of the country. It must however, be noted that
this is only a broad classification , since it is based on limited soil
Rating Chart for Soil Test Data
|Organic carbon ( as a measure of available
||Below o.5 %
||0.5 - 7.5%
|Available nitrogen( N)
||Below 10.0 Kg/ha
||Above 25 Kg/ha.
|Available potassium( K)
|Normal to saline
||6.0 to 8.5
|Tending to become alkaline
||8.9 to 9.0
Total Soluble Salts (Conductivity in milli mhos/cm2)
|critical for germination
||critical for growth of the sensitive
||Injurious to most crops
Infrastructure Related Information
Classification of Indian Soils
- There are 8 major group of soils in India which
are furnished below
- Red colour is due to various oxides of iron. They are
poor in N, P, K and with pH varying 7 to 7.5. These soils are light
textured with porous structure. Lime is absent with low soluble salts.
- Red soils occurs extensively in Andhra Pradesh
, Assam, Bihar, Goa, Parts of kerala, Maharastra, Karnataka, Tamilnadu
and West Bengal. Most of the red soils have been classified in the order
- Seen in high rainfall areas, under high rainfall conditions
silica is released and leached down wards and the upper horizons of
soils become rich in oxides of iron and alluminium. The texture is light
with free drainage structure.
- Clay is predominant and lime is deficient. pH 5 to
6 with low in base exchange capacity, contained more humus and are well
drained. They are distributed in summits of hills of Daccan karnataka,
Kerala, Madhyapradesh, Ghat regions of Orissa, Andhra pradesh, Maharastra
and also in West Bengal, Tamilnadu and Assam.
- Most of the laterite soils have bee classified
in the order ' ultisols' and a few under ' oxisols'.
- These are the most important soils
from the agriculture point of view. The soils are sandy loam to clay
loam with light grey colour to dark colour, structure is loose and more
fertile. But the soils are low in NPK and humus.
- They are well supplied with lime; base exchange
capacity is low, pH ranges from 7 to 8. These soils are distributed
in Indo-Gangetic plains, Brahmaputra valley and all most all states
of North and South. Most of the alluvial soils have been classified
in the orders ' Entisols', ' Inceptisols' and ' Alfisols'.
- This is well known group of soils characterised by
dark grey to black colour with high clay content.
- They are neutral to slightly alkaline in reaction.
Deep cracks develop during summer, the depth of the soil varies from
less than a meter to several meters. Poor free drainage results in the
soils, base exchange is high with high pH and rich in lime and potash.
Major black soils are found in Maharastra, Madhyapradesh, Gujarat and
- Cotton is most favourable crop to be grown in
these soils. These soils are classified in the order 'Entisols', ' Inceptisols'
and ' vertisols'.
- This group of soils occur in Himalayas. Soils
are dark brown with more sub-soil humus content. They are more acidic.
- These soils are mostly sandy to loamy fine sand with
brown to yellow brown colour, contains large amounts of soluble salts
and lime with pH ranging 8.0 to 8.5. Nitrogen content is very low.
- The presence of Phosphate and Nitrate make the
desert soils fertile and productive under water supply. They are distributed
in Haryana, Punjab, Rajasthan. They are classified in the order ' Aridisols'
and ' Entisols'.
Peaty and Marshy Soils
- These soils occur in humid regions with accumulation
of high organic matter. During monsoons the soils get submerged in water
and the water receipts after the monsoon during which period rice is
cultivated. Soils are black clay and highly acidic with pH of 3.5. Free
alluminium and ferrous sulphate are present.
- The depressions formed by dried rivers and lakes in
alluvial and coastal areas some times give rise to water logged soils
and such soils are blue in colour due to the presence of ferrous iron.
- Peaty soils are found more in Kerala and marshy
soils are found more in coastal tracks of Orissa, West Bengal and South
- East coast of Tamilnadu.
Saline - Sodic Soils
- Saline soils contain excess of natural soluble salts
dominated by chlorides and sulphates which affects plant growth. Sodic
or alkali soils contain high exchangeable sodium salts.
- Both kinds of salt effected soils occur in different
parts of India like Uttarpradesh, Haryana, Punjab, Maharastra, Tamilnadu,
Gujarat, Rajastan and Andhra pradesh. These soils are classified under
' Aridisols', ' Entisols' and ' Vertisols'.