Soil classification and Soil mineral types

1. AGRICULTURAL CHEMISTRY
Dr V. LATHA
AP/CHEMISTRY
SRI SRNM COLLEGE, SATTUR

2. SYLLABUS
UNIT I AGRICULTURAL CHEMISTRY
Soil classification:
genetic system of classification- modern system of
classification
Properties of soil:
soil minerals –primary and secondary minerals-
soil pH ,Soil acidity and alkalinity– effect of pH on
plants
Organic Manures- Farmyard manures- compost - Green manure.
Essential nutrients for plants:
Functions of Essential nutrients - Nitrogeneous fertilizers,
Phosphatic fertilizers, Potash fertilizers-Micro nutrients
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3. SOIL
 The mixture of inorganic
and organic solid ; air, water
and microorganisms.
 Soil is a life supporting
layer of material.
 It consists of a solid part
(core, mantle and crust) and
the atmosphere surrounding
it.
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4. SOIL CLASSIFICATION - Purpose
 Systematic study of soils
 Best use of soil
 Relationship between different kinds of soils
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5. SOIL CLASSIFICATION - Types
 Genetic System – based on origin
 Modern System – based on characteristics of soil
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6. GENETIC SYSTEM
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7. GENETIC SYSTEM-Orders
ZONAL It exhibits the properties determined by the
climate and vegetation
INTRA
ZONAL
Soil characteristics are influenced by the chemical
nature of parent material
AZONAL Recently deposited soil; so there is no well
developed profile.
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8. ZONAL SOILS- SUB ORDERS
Tundra
Soils
(soils of cold
zone)
Tundra soils are formed at high
latitudes .
It is very cold in the tundra.
Tundra soils are generally frozen
and rich in nitrogen and
phosphorus.
Desert
soils
(light colour
arid region)
Desert soils are mostly sandy soil
found in low rain fall regions .
It has low content of nitrogen and
organic matter with very high
CaCO3 and
Phosphate ,thus making it infertile.
Chestnut
Soils
(semi arid ,
humid
grassland)
Chestnut soil is an agriculturally
important group of Zonal soils
typically having dark brown surface
horizon that grades downward into
a lighter zone and into a horizon of
lime accumulation
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9. Degraded
chernozem soils
(soils of forest grasslands)
Chernozem soils contain
less humus, are more acid
and have inconvenient air
and water characteristics
Podzol soils
(soils of timber region)
Podzol soils area strongly
acid soils that usually have
a bleached horizon
immediately beneath the
top soil . This horizon is the
source of Al and Fe oxides
that have accumulated with
organic matter, reddish
coloured horizon
Lateritic soils
(forest warm tropical)
They are rock type rich
in Fe and Al.
Rusty red in colour ,due
to high iron oxide
content.
ZONAL SOILS- SUB ORDERS
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10. INTRA ZONAL -SUBORDERS
Hydromorphic
soils(saline and
alkaline) - excess
amount of water
Hydromorphic soils are
characterised by the reduction or
localised segregation of Fe,
owing to the temporary or
permanent waterlogging of the
soil pores which causes lack of O
over a long period
Halomorphic
soil(soil of
marshes,
swamps)-excess
amount of
soluble salts
A soil that contains a significant
proportion of soluble salts
Calcimorphic
soils(brown
forest soils) –
excess amount of
lime
This type of soils are found in the
surface of earth whose
characteristics are in large
related to the presence of lime
rich parent material of the soil.
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11. AZONAL SOILS –GREAT GROUPS
Lithosols Found on steep
slopes, stony soils
Regosols Develop from
mineral deposits
Alluvial soils
(brown forest
soils)
Formed by
weathering of rocks
(excess amount of
lime)
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12. MODERN SYSTEM
 USAD – United States Agricultural Department
 Taxonomy of soil
 Six levels of soil class
ORDER (10)
SUBORDER(47)
Great groups(185)
Sub Groups (970)
Family (4500)
Series(10,500)
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13. Characteristics of Soil Classification
1. It is a natural classification of soil.
2. The classification is based on properties of the soils.
3. The properties selected should be observable or measurable.
4. The properties selected should be those that either affect soil
genesis or result from soil genesis.
5. The properties with the greater significance to plant growth
should be selected for the higher category.
6. The classification system is flexible.
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14. MODERN SYSTEM – Soil Orders
 https://en.wikipedia.org/wiki/USDA_soil_taxonomy
 https://www.uidaho.edu/cals/soil-orders/alfisols
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15. MODERN SYSTEM – Soil Orders
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16. MODERN SYSTEM – Soil Sub Orders
Order suborder
Entisol Wassents, Aquents, Psamments, Fluvents and Orthents. (5)
Inceptisols Aquepts, Gelepts, Cryepts, Ustepts, Xerepts and Udepts (6)
Alfisols Aqualfs, Cryalfs , Udalfs , Ustalfs , Xeralfs (5)
Ultisols Aquults, Humults, Udults, Ustults and Xerults (5)
spodosols Aquods, Gelods, Cryods, Humods and Orthods (5)
Oxisols Aquox, Torrox, Ustox, Perox and Udox (5)
Aridisols Cryids, Salids, Durids, Gypsids, Argids, Calcids and Cambids
(7)
Vertisols Aquerts, Cryerts, Xererts, Torrerts, Usterts and Uderts (6)
Mollisols Albolls, Aquolls, Rendolls, Gelolls, Cryolls, Xerolls, Ustolls and
Udolls (8)
Histosols Folists, Wassists, Fibrists, Saprists and Hemists (5)
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17. Example of the Classification of a
Miami Silt Loam Soil:
 Order -Alfisol
 Sub-order -Udalf
 Great group -Hapludalf
 Sub-group -TypicHaludalf
 Family – Fine loamy, mixed
 Series – Miami
 Phase – Miami, eroded phase
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18. SOIL PROPERTIES
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19. SOIL PROPERTIES
 Soil Texture
 Soil Water
 Soil Temperature
 Soil Colloids
 Soil Minerals
 Soil pH, soil acidity and alkalinity
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20. SOIL MINERALS
 A soil derived from minerals or rocks and containing little
humus or organic matter.
 Soil minerals play a vital role in soil fertility.
 Different types of soil minerals hold and retain differing
amounts of nutrients.
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21. TYPES OF SOIL MINERALS
Primary Minerals
Secondary Minerals
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22. PRIMARY MINERALS
 The primary minerals are those which are formed owing
to the crystallization of the molten magma.
 The original grains or mineral crystals which can be
seen in the soil with the naked eye.
 Ex: Feldspar, mica, silica, iron oxides,
aluminium oxides
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23. SECONDARY MINERLS
 Formed at the earth’s surface by weathering on the
pre-existing primary minerals under variable
conditions of temperature and pressure.
 During weathering, water accompanied by
CO2 from the atmosphere plays an important role
in processes, like hydrolysis, hydration and
solution.
 Ex: Carbonates, Phosphates, Zircon, Pyrites
Feldspar + water clay mineral + cations +
anions + soluble silica
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24. Primary Minerals - Feldspar
 Feldspar are made up of sodium, calcium, potassium
silicates.
 Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are
a group of rock-forming tectosilicate minerals that
make up about 41% of the Earth's continental crust by
weight.
 Feldspars crystallize from magma as both intrusive
and extrusive igneous rocks and are also present in
many types of metamorphic rock.
 Harder then a steel knife blade.
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25. Primary Minerals - Mica
 Mica are distributed in rocks as
silicates of K and Mg, Na and Li.
 They are all silicate minerals,
known as sheet silicates because
they form in distinct layers.
 Muscovite – White Mica -
KAl₂(F,OH)₂,
KF)₂(Al₂O₃)₃(SiO₂)₆.
 Biotite - Black mica-
 K(Mg,Fe)3AlSi3O10(F,OH)
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26. Primary Minerals - Mica
 Micas are fairly light and relatively soft, and the
sheets and flakes of mica are flexible.
 Mica is heat-resistant and does not conduct
electricity.
 There are 37 different mica minerals.
 The most common include:
 purple lepidolite, black biotite,
 brown phlogopite and clear muscovite.
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27. Primary Minerals - Silica
 Silicon dioxide, also known as silica, is an oxide of silicon
with the chemical formula SiO2
 Most commonly found in nature as quartz and in various
living organisms.
 In many parts of the world, silica is the major constituent
of sand.
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28. Primary Minerals – Iron oxides
 Iron oxides are chemical compounds composed
of iron and oxygen. There are sixteen known iron
oxides and oxyhydroxides, the best known of which is
rust, a form of iron(III) oxide.
 Iron oxides and oxyhydroxides are widespread in
nature and play an important role in many geological
and biological processes.
 Magnetite, Hematite,
 Goethite, limonite
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29. Primary Minerals – Aluminium oxides
 Aluminium oxide is a chemical compound
of aluminium and oxygen with the chemical formula
Al2O3.
 It is the most commonly occurring of several aluminium
oxides, and specifically identified
as aluminium(III) oxide.
 Corundum,
 Diaspore,
 Gibbsite
Diaspor
e
Gibbsite
Corundum
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30. Secondary Minerals – Carbonates
 Main carbonate minerals found in soil are Ca, Mg
and Fe.
Ore Formula
Calcite CaCO3
Magnesite MgCO3
Dolomite MgCO3·CaCO
3
Siderite FeCO3
Calcite Magnesite
Dolomite Siderite
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31. Secondary Minerals – Carbonates
 Very soft
 Dissolves in acid
 Calcite – major constituent of marble
 Lime stones are used to neutralize soil acidity.
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32. Secondary Minerals – Phosphates
 Apatite – contains P,
occurs in igneous rock as
small crystals.
 Strendite – Iron phosphate
It is an important plant nutrient mineral.
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33. Secondary Minerals – Zircon
 It is Zirconium
silicate with a chemical
composition of ZrSiO4.
 It is common throughout
the world as a minor
constituent of igneous,
metamorphic,and
sedimentary rocks.
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34. Secondary Minerals – Pyrites
 A shiny yellow mineral consisting of iron disulphide
and typically occurring as intersecting cubic crystals.
 Pyrite used to be an important ore for the production
of sulfur and sulfuric acid.
 Today most sulfur is obtained as a byproduct of oil
and gas processing.
 Some sulfur continues to be produced from pyrite as a
byproduct of gold production.
 Pyrite is occasionally used as a gemstone.
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35. Secondary Minerals – Pyrites
 It is an iron mineral
 Fool’s gold due to its yellow appearance
 Source of Fe and S in plant nutrition.
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36. Secondary Minerals – Clay Minerals
 Clay minerals are hydrous aluminium phyllosilicates,
sometimes with variable amounts of iron, magnesium,
alkali metals, alkaline earths, and other cations found
on or near some planetary surfaces.
 Formed by weathering of Feldspar, mica and silicates.
 Occur abundantly in soils and rocks.
 Have high chemical activity.
 Strong adhesive and water holding force.
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37. SOIL pH, SOIL ACIDITY and SOIL
ALKALINITY
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38. SOIL pH
 Soil pH or soil reaction is an indication of the acidity
or alkalinity of soil and is measured in pH units.
 Soil pH is defined as the negative logarithm of the
hydrogen ion concentration.
 The pH scale goes from 0 to 14 with pH 7 as the
neutral point.
 As the amount of hydrogen ions in the soil increases
the soil pH decreases thus becoming more acidic.
 From pH 7 to 0 the soil is increasingly more acidic
 From pH 7 to 14 the soil is increasingly more alkaline
or basic.
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39. SOIL pH
 Soil pH is considered a master variable in soils as
it affects many chemical processes.
 It specifically affects plant nutrient availability by
controlling the chemical forms of the different
nutrients and influencing the chemical reactions
they undergo.
 The optimum pH range for most plants is between
5.5 and 7.5;
 However, many plants have adapted to thrive at
pH values outside this range.
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40. pH – common examples
Descriptive terms commonly associated with certain ranges in soil pH are:
 Extremely acid: < than 4.5; lemon=2.5; vinegar=3.0; stomach acid=2.0; soda=2–4
 Very strongly acid: 4.5–5.0; beer=4.5–5.0; tomatoes=4.5
 Strongly acid: 5.1–5.5; carrots=5.0; asparagus=5.5; boric acid=5.2; cabbage=5.3
 Moderately acid: 5.6–6.0; potatoes=5.6
 Slightly acid: 6.1–6.5; salmon=6.2; cow's milk=6.5
 Neutral: 6.6–7.3; saliva=6.6–7.3; blood=7.3; shrimp=7.0
 Slightly alkaline: 7.4–7.8; eggs=7.6–7.8
 Moderately alkaline: 7.9–8.4; sea water=8.2; sodium bicarbonate=8.4
 Strongly alkaline: 8.5–9.0; borax=9.0
 Very strongly alkaline: > than 9.1; milk of magnesia=10.5, ammonia=11.1; lime=12
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41. pH Levels
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43. Soil Acidity
Soils tend to become acidic as a result of:
 Rainwater leaching away basic ions (calcium, magnesium,
potassium and sodium);
 CO2 from decomposing organic matter and root respiration
dissolving in soil water to form a weak organic acid;
 Formation of strong organic and inorganic acids, such as nitric
and sulfuric acid, from decaying organic matter and oxidation
of ammonium and sulfur fertilizers.
 Soil acidification is a natural process that is accelerated by
acids produced in soil by most nitrogen fertilizers.
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44. Soil Acidity - Reason
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45. Soil Acidity - Problems
 Aluminum and manganese are more soluble and can
be toxic to plants;
 Calcium, magnesium, potassium, phosphorus, or
molybdenum (especially needed for nitrogen fixation
by legumes) may be deficient; and
 Decomposition of soil organic matter is slowed and
causes decreased mineralization of nitrogen.
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46. Soil Acidity – Organic Matter
 The problems caused by soil acidity are usually less
severe, and the optimum pH is lower, if the soil is well
supplied with organic matter.
 Organic matter helps to make aluminum less toxic.
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47. Soil Acidity –organic matter
 Soil organic matter slows down acidification and
buffers the soil’s pH because it holds the acid hydrogen
tightly.
 Therefore, more acid is needed to decrease the pH by a
given amount when a lot of organic matter is present.
 Of course, the reverse is also true - more lime is needed
to raise the pH of high-organic-matter soils by a given
amount.
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48. Soil Alkalinity
 Lime is usually added to acid soils to increase soil pH.
 The addition of lime not only replaces hydrogen ions and
raises soil pH, thereby eliminating most major problems
associated with acid soils but it also provides two
nutrients, calcium and magnesium to the soil.
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49. Soil Alkalinity
Some common liming materials are:
 Calcic limestone which is ground limestone;
 Dolomitic limestone from ground limestone high in
magnesium;
 Miscellaneous sources such as wood ashes.
 Liming materials are relatively inexpensive,
comparatively mild to handle and leave no objectionable
residues in the soil.
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50. Soil Alkalinity
Limestone application helps create a more hospitable soil for
acid-sensitive plants in many ways, such as the following:
 by neutralizing acids;
 by adding calcium in large quantities (because limestone is
calcium carbonate, CaCO3);
 by adding magnesium in large quantities if dolomitic limestone
is used (containing carbonates of both calcium and
magnesium);
 by making molybdenum and phosphorus more available;
 by helping to maintain added phosphorus in an available form;
 by enhancing bacterial activity, including the rhizobia that fix
nitrogen in legumes; and
 by making aluminum and manganese less soluble.
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51. Soil Alkalinity - Sources
Total soil alkalinity increases with:
 Weathering of silicate, aluminosilicate and carbonate minerals
containing Na+ ,Ca2+ , Mg2+ and K+;
 Addition of silicate, aluminosilicate and carbonate minerals to
soils;
 Addition of water containing dissolved bicarbonates (as occurs
when irrigating with high-bicarbonate waters).
 The accumulation of alkalinity in a soil (as carbonates and
bicarbonates of Na, K, Ca and Mg) occurs when there is
insufficient water flowing through the soils to leach soluble
salts.
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52. Soil Alkalinity - Sources
 This may be due to arid conditions, or poor internal
soil drainage; in these situations most of the water that
enters the soil is transpired (taken up by plants) or
evaporates, rather than flowing through the soil.
 The soil pH usually increases when the
total alkalinity increases, but the balance of the added
cations also has a marked effect on the soil pH.
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53. Soil Alkalinity - Sources
 For example, increasing the amount of sodium in
an alkaline soil tends to induce dissolution
of calcium carbonate, which increases the pH.
 Calcareous soils may vary in pH from 7.0 to 9.5
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