Soil chemistry and soil type

GROUP MEMBERS:
Anum Mehnaz (938)
Saman Rubab (964)
Sadaf Attique (961)
Ayesha Sagheer (945)
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Content:
 Soil chemistry
 Classification of soil
 Horizons of soil
 Soil colour
 Soil naming ,soil air,PH
 Instrument used to monitor soil moisture
 Physicochemical properties of soil
 Soil chemistry in relation with environment
 Conclusion
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Soil:
The organic and inorganic materials on the surface of the earth that
provide the medium for plant growth.
Soil Chemistry:
A scientific discipline dealing with chemical properties of soils and studies
on the influence of fertilizers, pesticides and the other chemical substances
applied on or into the soil on soil behaviour and fertility.
 https://study.com/academy/lesson/what-is-soil-definition-structure-types.html
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Classificationof Soil:
1. Alfisol
2. Mollisol
3. Ultisol
4. Spodosol
5. Aridisol
Alfisol:
 Alfisols are arable soils with water content adequate for at least three consecutive months
of the growing season.
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Mollisol:
 A soil of an order comprising temperate grassland soils with a dark, humus-rich surface layer
containing high concentrations of calcium and magnesium.
Ultisol:
 A highly weathered leached red or reddish-yellow acid soil with a clay-rich B horizon,
occurring in warm, humid climates.
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Spodosol:
 Spodosol are ashy gray, acidic soils with a strongly leached surface layer.
 Their suitability for cultivation is limited to acid-tolerant crops and orchards, provided
that sufficient lime and fertilizer are applied.
Aridisol:
 A soil of an order comprising typically saline or alkaline soils with very little organic
matter, characteristic of arid regions.
 https://www.britannica.com/science/Alfisol
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 Soil has three main
horizons which are
A, B and C but we
also consider O,E
and R also.
Horizons of soil:
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Soil colour:
 The main pigmenting agents in soils are organic matter, iron, and, to a lesser
extent, manganese.
 When these agents are not covering the mineral grains, the natural color of
the grains is visible.
Soil naming:
 Soils are named and classified on the basis of physical and chemical properties
in their horizons (layers).
 Soil Taxonomy” uses color, texture, structure, and other properties of the soil.
 https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/soil-color
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Soil Air:
 The volume of the soil that is not occupied by soil particles is known as ‘Pore Space’
which means soil air.
 The pore space is usually occupied by air and water.
 The air filled pores constitute the gaseous phase of the soil system.
 Oxygen is essential for all biological reactions occurring in soil.
 Soil air differs from atmospheric air by having a higher carbon dioxide and lower
oxygen content.
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Soil pH:
 The acidity or alkalinity of a substance is measured in pH
units, a scale running from 0 to 14. A pH of 7 is neutral.
 As numbers decrease from 7, the acidity gets higher.
 As numbers increase from 7 so does the alkalinity.
 Soil pH generally range from an extremely acidic pH of 3
to a very alkaline pH of 10.
 Most cultivated plants enjoy slightly acidic conditions
with a pH of about 6.5.
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Instrument used to monitor the soilmoisture:
 Tensiometer is used for
the monitoring of soil
moisturization..
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1. Physical Properties
a. Structure of soil:
 It refers to the arrangement of soil separates into units called soil aggregates.
 An aggregate possesses solids and pore space.
 The aggregate acts like a larger silt or sand particle depending upon its size
b. Soil Density:
 Soil density is expressed in two concepts as particle density and bulk density.
 Particle density:
 The weight per unit volume of the solid portion of soil is called particle density.
 Particle density can be expressed in terms of grams per cubic meter (g/m3).
 Generally particle density of normal soils is 2.65 grams per cubic meter.
 Particle density is also termed as true density.
Physicochemical reactions of Soil:
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Textural classes Particle density ( g/ cm3)
Coarse sand 2.655
Fine sand 2.659
Silt 2.798
Clay 2.837
Textural classes Particle density ( g/ cm3)
Coarse sand 2.655
Fine sand 2.659
Silt 2.798
Clay 2.837
Particledensityof differentsoiltexturalclasses.
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BulkDensity:
 The oven dry weight of a unit volume of soil inclusive of pore spaces is called bulk density.
 The bulk density of a soil is always smaller than its particle density.
 Bulk density normally decreases, as mineral soils become finer in texture.
 The bulk density varies indirectly with the total pore space present in the soil and gives a
good estimate of the porosity of the soil.
Textural class Bulk density (g/cm3) Pore space (%)
Sandy soil 1.6 40
Loam 1.4 47
Silt loam 1.3 50
Clay 1.1 58
Bulkdensityof differenttextural classes.
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c. Porosity of Soil:
 A soil's porosity and pore-size distribution characterize its pore space, that portion of the soil's
volume that is not occupied by solid material.
 The basic character of the pore space governs critical aspects of almost everything that occurs in the
soil, the movement of water, air, and other fluids; the transport and the reaction of chemicals; and the
residence of roots and other biota.
d. Temperatureof Soil:
 Soil temperature is required for calculating most belowground ecosystem processes, including root
growth and respiration, decomposition, and nitrogen mineralization.
 Mean annual soil temperatures are 2–4°C warmer than mean annual air temperatures.
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e. Soil Plasticity:
 Soil Plasticity is the property of soil by which it undergoes deformation without cracking or
fracturing.
 The adsorbed water contributes to the plasticity of the soil since it allows the clay particles to slip
over one another.
f. SoilCompressibility:
 Soil Compressibility refers to the tendency of soil to consolidate or decrease in volume.
 The compressibility is partly a function of elastic nature of soil particles and is directly related to
settlement of structures.
 Coarse materials such as gravels and sands have low compressibility and the settlement is
considerably less in these materials as compared to highly compressible fine grained organic soils.
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g. Soil Erodibility:
 It refers to the ease with which soil materials can be removed by wind or water.
 Easily eroded materials include unprotected silt, sand and other loosely consolidated
materials, cohesive soils (with more than 20% clay) and naturally cemented soils are not
easily removed from its place by wind or water and, therefore, have a low erosion factor.
 http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447039&topicorder=4&maxto=10
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1. Chemical Properties
a. Inorganic matters of Soil:
 Compounds of aluminium, silicon, calcium, magnesium, iron, potassium and sodium are chief
inorganic constituents of soils.
 Chemical composition of soil of one horizon differs greatly from the composition of soil in the other
horizon.
b. Organic matters of soil:
 Organic component of the soil consists of substances of organic origin; living and dead.
 In sandy soil of arid zone, it is found in very poor quantity (one or less than one per cent) but in peaty
soil, it may be as high as 90%.
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c. Buffer Action:
 Buffer action of soil chemistry refers to the resistance to change in pH of a system.
 property of soil to resist a change in pH is called “buffer action”.
 Buffer solutions are usually formed of a mixture of salt of weak acid and acid itself.
d. Buffering in soil:
 Soils should have good buffering capacity Therefore, it is necessary to add considerably large
amount of acids or alkalis in order to bring about any change in the original pH of soil.
 Phosphates, carbonates, bicarbonates and other salts of weak inorganic acids are important
buffering agents in the soils.
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Soil Chemistry in relation withEnvironment:
 Soil chemistry has traditionally focused on the chemical reactions in soils that affect plant growth
and plant nutrition.
 However, beginning in the 1970s and certainly in the 1990s, as concerns increased about inorganic
and organic contaminants in water and soil and their impact on plant, animal, and human health, the
emphasis of soil chemistry is now on environmental soil chemistry.
 Environmental soil chemistry is the study of chemical reactions between soils and
environmentally important plant nutrients, radionuclides, metals, metalloids, and organic
chemicals.
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Conclusions:
 Soil is one of the most important natural resources and study about Soil Chemistry is not only
interesting but also a challenging. It is the heart of the terrestrial ecological system so
understanding of the soil system is the key to the success and environmental harmony of any
human use of the land.
 https://www.researchgate.net/publication/216656462_Concise_Soil_Chemistry
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Soil chemistry and soil type

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