Science of soil


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  • SCIENCE OF SOIL


A collection of natural bodies developed in the unconsolidated mineral and organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants and has properties due to the effects of climate and living matter acting upon parent material, as conditioned by topography, over a period of time.

  • A collection of natural bodies developed in the unconsolidated mineral and organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants and has properties due to the effects of climate and living matter acting upon parent material, as conditioned by topography, over a period of time.



Rocks are chief sources for the parent material over which soils are developed

  • Rocks are chief sources for the parent material over which soils are developed

  • Types of rocks-

  • Igneous

  • Sedimentary

  • Metamorphic

  • Genesis includes –weathering of rocks & formation of soil



Primary Minerals: Minerals that have persisted with little change in composition since they were extruded in molten lava(eg. quartz, mica and feldspars).They are most prominent in sand and silt fractions.

    • Primary Minerals: Minerals that have persisted with little change in composition since they were extruded in molten lava(eg. quartz, mica and feldspars).They are most prominent in sand and silt fractions.
    • Secondary Minerals: Minerals such as the silicate clays and iron oxides, have been formed by the breakdown and weathering of less resistant minerals as soil formation progressed.


It is physical and chemical disintegration and decomposition of rocks. Weathering creates the parent material over which the soil formation takes place. Later weathering, soil formation and development proceeds simultaneously.

  • It is physical and chemical disintegration and decomposition of rocks. Weathering creates the parent material over which the soil formation takes place. Later weathering, soil formation and development proceeds simultaneously.



Temperature

  • Temperature

  • Water

  • Wind

  • Plants & animals



Solution

  • Solution

  • Hydration

  • Hydrolysis

  • Acidification

  • Oxidation

  • Reduction



Chemical weathering

  • Chemical weathering

  • As soon as physical disintegration of rock and mineral begins, chemical decomposition starts.

  • Water and its solution – hydrolysis, hydration, dissolution

  • KAlSi3O8 + H2O ------> HAlSi3O8 + K+ + OH-

  • 2 HAlSi3O8 + 11 H2O ---- Al2O3 + 6 H4SiO4

  • Al2O3 + 3H2O ----- Al2O3.3H2O

  • Acid solution weathering

  • CaCO3 + H2CO3 -----> Ca2+ + 2 HCO3-



Oxidation

  • Oxidation

  • 3 MgFeSiO4 + 2 H2O H4Mg3Si2O9 + SiO2 + 3FeO

  • 4 FeO + O2 + 2 H2O -- 4 FeOOH

  • It is particularly manifest in rocks containing iron



The mineral weathering combines with the associated physical and chemical phenomena constitute the process of soil formation.

  • The mineral weathering combines with the associated physical and chemical phenomena constitute the process of soil formation.

  • It includes-

  • The addition of organic & mineral materials

  • The loss of these materials from the soil

  • Translocation of materials from one point to Another within the soil column

  • Transformation of minerals & organic substances within the soil



Pedological

  • Pedological

  • Edaphological







1941: soil is open system, properties are functionally related; system changes when property(ies) change(s).

  • 1941: soil is open system, properties are functionally related; system changes when property(ies) change(s).

  • Jenny’s CLORPT equation

    • s = ƒ (cl, o, r, p, t)








Moisture

  • Moisture

    • Chemical and biological activities
    • Excess precipitation – eluviation and illuviation
    • Excess evaporation – capillary action


Vegetation

  • Vegetation

    • Provide humus, bind soil and counteract percolation by transpiration
    • Maintain fertility
    • Different types of vegetation require different proportions of bases.
    • Tree: little calcium and magnesium
    • Grass: much calcium and magnesium


Examination of a vertical section of a soil as seen in a roadside cut or in the walls of a pit dug in the field, reveals the presence of more or less distinct horizontal layers. Such a section is called a profile, and the individual layers are known as horizons

  • Examination of a vertical section of a soil as seen in a roadside cut or in the walls of a pit dug in the field, reveals the presence of more or less distinct horizontal layers. Such a section is called a profile, and the individual layers are known as horizons





When a soil is ploughed and cultivated, the natural state of the upper 12-18 centimeters(5-7 inches) is modified. This manipulated part of the soil is referred to as the surface soil or the topsoil.

  • When a soil is ploughed and cultivated, the natural state of the upper 12-18 centimeters(5-7 inches) is modified. This manipulated part of the soil is referred to as the surface soil or the topsoil.

  • The subsoil is comprised of those soils layers underneath the top soil.



Mineral soils: Mineral or inorganic in composition, low in organic matter ranges from 1 -6%.

  • Mineral soils: Mineral or inorganic in composition, low in organic matter ranges from 1 -6%.

  • Organic soils: 50% organic matter by volume (at least 20% by weight).



Soil Texture: Proportions of different sized particles present in soil.

  • Soil Texture: Proportions of different sized particles present in soil.

  • Soil Structure: The arrangement of the sand silt and clay particles within the soil.





Soil air differs from the atmospheric air in several respects-

  • Soil air differs from the atmospheric air in several respects-

  • First ,the composition of soil air is quite dynamic and varies greatly from place to place within a given soil.

  • Second, soil air generally has a higher moisture content than the atmosphere; the relative humidity of soil air approaches 100% when the soil moisture is optimum.

  • Third, carbon dioxide in soil air is often several times higher than the 0.03% commonly found in the atmosphere, Oxygen decreases accordingly and, in extreme cases 5-10%, or even less, as compared to about 20% for normal atmosphere.





Soil organic matter comprises an accumulation of partially disintegrated and decomposed plant and animal residues and other organic compounds synthesized by the soil microbes as the decay occurs. Such material is continually being broken down and re-synthesized by soil microorganisms. Consequently, organic matter is a rather transitory soil constituent, lasting for a few hours to several hundred years.

  • Soil organic matter comprises an accumulation of partially disintegrated and decomposed plant and animal residues and other organic compounds synthesized by the soil microbes as the decay occurs. Such material is continually being broken down and re-synthesized by soil microorganisms. Consequently, organic matter is a rather transitory soil constituent, lasting for a few hours to several hundred years.

  • Organic matter binds mineral particles into granules that are largely responsible for the loose. easily managed condition of productive soils and increases the number of water a soil can hold.

  • It is also major soil source of phosphorus and sulfur and the primary source of nitrogen (3 elements essential for plant growth)



Organic matter, including plant and animal residues, is the main source of energy for soil organisms. Without it biochemical activity would come to a near standstill.

  • Organic matter, including plant and animal residues, is the main source of energy for soil organisms. Without it biochemical activity would come to a near standstill.

  • In addition to the original plant and animal residues and to their partial breakdown products, soil organic matter includes complex compounds that are relatively resistant to decay. These complex materials, along with some that are synthesized by the soil microorganisms, are collectively known as humus. This material is usually black and brown in colour, is very fine(colloidal) in nature.



Water is hold in the soil for varying degree of tenacity depending on the amount of water present and the size of the pores.

  • Water is hold in the soil for varying degree of tenacity depending on the amount of water present and the size of the pores.

  • Together with its soluble constituents, including nutrient elements(eg. Ca, P, N and K), soil water makes up the soil solution, which is the critical medium for supplying nutrients to growing plants.

  • The movement can be in any direction; downward in response to gravity, upward as water moves to the soil surface to replace that lost by evaporation, and in any direction toward plant roots as they absorb this important liquid. Although some of the soil moisture is removed by the growing plants, some remains in the tiny pores and in thin films around soil particles. The soil solids strongly attract the soil water and consequently compete for it with plant roots.



The soil solution contains small but significant quantities of soluble inorganic and organic compounds, some of which contain elements that are essential for plant growth

  • The soil solution contains small but significant quantities of soluble inorganic and organic compounds, some of which contain elements that are essential for plant growth

  • Critical property of the soil solution is its acidity or alkalinity. Many chemical and biological reactions are dependent on the levels of hydrogen ions and hydroxide ions in the soil. These levels influence the solubility, and in turn the availability to plants, of several essential nutrient elements such as Fe, Mn, P, Zn and Mo.



The concentration of hydrogen(H+) and hydroxide ions(OH-) in the soil solution is commonly ascertained by determining its pH. Technically the pH is the negative logarithm of the concentration of hydrogen ion in the soil solution. Thus each unit change in pH represents a tenfold change in the activity of the H+ and OH- ions.

  • The concentration of hydrogen(H+) and hydroxide ions(OH-) in the soil solution is commonly ascertained by determining its pH. Technically the pH is the negative logarithm of the concentration of hydrogen ion in the soil solution. Thus each unit change in pH represents a tenfold change in the activity of the H+ and OH- ions.

  • Acidity Alkalinity



The attraction of ions such as Ca2+, Mg2+, and K+ on the surfaces of colloidal clay and humus is not as exciting as is the exchange of these ions for other ions in the soil solution. For example, an H+ ion released to the soil solution by a plant root exchange readily with a potassium ion(K+) adsorbed on the colloidal surface .The K+ ion is then available in the soil solution for uptake by the roots of crop plants. A simple example of such cation exchange illustrates this point.

  • The attraction of ions such as Ca2+, Mg2+, and K+ on the surfaces of colloidal clay and humus is not as exciting as is the exchange of these ions for other ions in the soil solution. For example, an H+ ion released to the soil solution by a plant root exchange readily with a potassium ion(K+) adsorbed on the colloidal surface .The K+ ion is then available in the soil solution for uptake by the roots of crop plants. A simple example of such cation exchange illustrates this point.

  • K+ + H+(aq) H+ + K+(aq) (adsorbed) (in soil solution) (adsorbed) (in soil solution)











Land degradation is a concept in which the value of the biophysical environment is affected by one or more combination of human-induced processes acting upon the land. It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable. Natural hazards are excluded as a cause, however human activities can indirectly affect phenomena such as floods and bushfires.

  • Land degradation is a concept in which the value of the biophysical environment is affected by one or more combination of human-induced processes acting upon the land. It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable. Natural hazards are excluded as a cause, however human activities can indirectly affect phenomena such as floods and bushfires.

  • It is estimated that up to 40% of the world's agricultural land is seriously degraded.



The major causes include:

  • The major causes include:

  • Land clearance, such as clear cutting and deforestation

  • Agricultural depletion of soil nutrients through poor farming practices

  • Overgrazing

  • Inappropriate Irrigation and over-drafting

  • Urban sprawl and commercial development

  • Land pollution including industrial waste

  • .



Vehicle off-roading

  • Vehicle off-roading

  • Quarrying of stone, sand, ore and minerals Overcutting of vegetation

  • Overgrazing

  • shifting cultivation without adequate fallow periods, absence of soil conservation measures,

  • Population pressure



The major stresses on vulnerable land include:

  • The major stresses on vulnerable land include:

  • Accelerated soil erosion by wind and water

  • Soil acidification and the formation of acid sulfate soil resulting in barren soil

  • Soil alkalinisation owing to irrigation with water containing sodium bicarbonate leading to poor soil structure and reduced crop yields

  • Soil salinization in irrigated land requiring soil salinity control to reclaim the land

  • Waterlogging in irrigated land which calls for some form of subsurface land drainage to remediate the negative effects

  • Destruction of soil structure including loss of organic matter

  • Ultimately results into low vegetation cover, extensive soil erosion which leads towards desertification



  • Every year 84 billion tonnes of productive top soil are lost world wide through degradation.

  • Degradation has already affected 1900 m ha of land globally (De Man et. al. 2007).

  • Additionally each year over 14 million acres of productive lands are oversalted because of improper water management.



Soil erosion is the process of detachment of soil particles from the parent body and transportation of the detached soil particles by wind or water.

  • Soil erosion is the process of detachment of soil particles from the parent body and transportation of the detached soil particles by wind or water.

  • Mechanism of Water Erosion:

  • Detachment

  • Transportation

  • Causes:

  • Natural

  • Anthropogenic



Sheet Erosion: uniform removal of top soil in thin layer from the field, least conspicuous.

  • Sheet Erosion: uniform removal of top soil in thin layer from the field, least conspicuous.

  • Rill Erosion: channelization begins ,no longer uniform.

  • Gully Erosion: unchecked rills result in increased channelization of runoff.

  • Ravines: manifestation of prolonged process of gully erosion. Deepening & Widening of gullies used to form ravines.

  • Landslides: occur in mountain slopes when the slope exceeds 20 per cent and width 6 m.

  • Stream-bank Erosion: Seasonal streams or rivulets often change their course from season to season due to blockage of their previous course by transported rocks, clods of soil & vegetation grown during lean periods.









Suspension- Most spectacular method of transporting soil particles is by suspension. Dust particles of fine sand ( less than 0.1 mm dia) are moved parallel to ground surface and upward. About 5-15 % of wind erosion afftected soil is transported by this process.

  • Suspension- Most spectacular method of transporting soil particles is by suspension. Dust particles of fine sand ( less than 0.1 mm dia) are moved parallel to ground surface and upward. About 5-15 % of wind erosion afftected soil is transported by this process.

  • Saltation- Particles in the range 0.1-0.5 mm diameter are lifted by the wind, then fall back to the ground, so they move in a hopping or bouncing fashion. These particles cause abrasion of the soil surface and as they hit other particles they break into smaller particles, a process called attrition. Depending on conditions, this process may account for 50-70% of the total movement of soil.

  • Surface creep- Rolling and sliding of larger particles (more than 0.5 mm dia) along the surface. Surface creep account to 5-25% of total movement due to action of wind.





Definition

  • Definition

  • Soil conservation is using and managing land based on the capabilities of the land itself.



Agronomic Measures

  • Agronomic Measures

  • Contour Cultivation – By ploughing and sowing across the slope, each ridge of plough furrow and each row of the crop act as an obstruction to runoff, providing more opportune time for water to enter into the soil and reduce soil loss.

  • Tillage – Tillage alters soil physical characters like porosity, bulk density, surface roughness and hardness of pans. Conventional tillage includes ploughing twice or thrice followed by some secondary operations like harrowing and planking that smoothen and pack the soil in seed-bed and/or control weeds.

  • Mulching – Mulches are any material such as straw, plant residues, leaves, loose soil or plastic film placed on the soil surface to reduce evaporation, erosion or to protect plant roots from extremely low or high temperature.



Contour Bunding – Runoff from any given surface is along the line of greatest slope and the velocity of runoff increases with the vertical distance through which it is moved. The contour bund being on the same elevation, assures that the depth of water against the bund is uniform throughout its length. It ensures uniform distribution of water above the bunds and therefore, better cultivation possibilities than any other type of bund. As the bunds are at regular intervals, they intercept the runoff from attaining erosive velocity and causing erosion. The velocity of flowing water is slowed down and water thus held on the field for a longer time, soaks into the soils.

  • Contour Bunding – Runoff from any given surface is along the line of greatest slope and the velocity of runoff increases with the vertical distance through which it is moved. The contour bund being on the same elevation, assures that the depth of water against the bund is uniform throughout its length. It ensures uniform distribution of water above the bunds and therefore, better cultivation possibilities than any other type of bund. As the bunds are at regular intervals, they intercept the runoff from attaining erosive velocity and causing erosion. The velocity of flowing water is slowed down and water thus held on the field for a longer time, soaks into the soils.

  • Broad Base Terrace - A terrace is a combination of ridge and channel built across the slope. These terraces have wide base and low height of ridge and usually formed with machinery. BBTs are constructed in soils with high clay content which develop deep cracks in summer (e.g. Black soil).







Grasses prevent soil erosion by intercepting rainfall, by binding the soil particles and by improving soil structure. A grass-legume association is ideal for soil conservation. E.g Pennisetum pupureum, Cenchrus ciliaris, Setaria sphacelata.

  • Grasses prevent soil erosion by intercepting rainfall, by binding the soil particles and by improving soil structure. A grass-legume association is ideal for soil conservation. E.g Pennisetum pupureum, Cenchrus ciliaris, Setaria sphacelata.

  • Forestry Measure

  • Afforestation and re-forestation in wastelands





















Waste (also known as rubbish, trash, refuse, garbage, junk, litter, and ort) is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea and sweat.

    • Waste (also known as rubbish, trash, refuse, garbage, junk, litter, and ort) is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea and sweat.
  • Basel Convention Definition of Wastes

  • “substances or objects which are disposed of or are intended to be disposed of or are required to be disposed of by the provisions of the law”

  • Disposal means

  • “any operation which may lead to resource recovery, recycling, reclamation, direct re-use or alternative uses (Annex IVB of the Basel convention)”



The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal, usually known simply as Basel Convention, is an international treaty that was designed to reduce the movements of hazardous waste between nations, specially to prevent transfer of hazardous waste from developed to less developed countries (LDCs). It does not, however, address the movement of radioactive waste. The convention is also intended to minimize the amount and toxicity of wastes generated, to ensure their environmentally sound management as closely as possible to the source of generation, and to assist LDCs in environmentally sound management of the hazardous and other wastes they generate.

  • The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal, usually known simply as Basel Convention, is an international treaty that was designed to reduce the movements of hazardous waste between nations, specially to prevent transfer of hazardous waste from developed to less developed countries (LDCs). It does not, however, address the movement of radioactive waste. The convention is also intended to minimize the amount and toxicity of wastes generated, to ensure their environmentally sound management as closely as possible to the source of generation, and to assist LDCs in environmentally sound management of the hazardous and other wastes they generate.

  • The Convention was opened for signature on 22nd March 1989, and entered into force on 5 May 1992.



Global solid waste composition

  • Global solid waste composition



Bio-degradable

  • Bio-degradable

  • can be degraded (paper, wood, fruits and others)

  • Non-biodegradable

  • cannot be degraded (plastics, bottles, old machines,cans, styrofoam containers and others)



Hazardous wastes

  • Hazardous wastes

  • Substances unsafe to use commercially, industrially, agriculturally, or economically and have any of the following properties- ignitability, corrosivity, reactivity & toxicity.

  • Non-hazardous

  • Substances safe to use commercially, industrially, agriculturally, or economically and do not have any of those properties mentioned above. These substances usually create disposal problems.



Municipal Solid wastes: Solid wastes that include household garbage, rubbish, construction & demolition debris, sanitation residues, packaging materials, trade refuges etc. are managed by any municipality.

  • Municipal Solid wastes: Solid wastes that include household garbage, rubbish, construction & demolition debris, sanitation residues, packaging materials, trade refuges etc. are managed by any municipality.

  • Bio-medical wastes: Solid or liquid wastes including containers, intermediate or end products generated during diagnosis, treatment & research activities of medical sciences.

  • Industrial wastes: Liquid and solid wastes that are generated by manufacturing & processing units of various industries like chemical, petroleum, coal, metal gas, sanitary & paper etc.

  • Agricultural wastes: Wastes generated from farming activities. These substances are mostly biodegradable.

  • Fishery wastes: Wastes generated due to fishery activities. These are extensively found in coastal & estuarine areas.

  • Radioactive wastes: Waste containing radioactive materials. Usually these are byproducts of nuclear processes. Sometimes industries that are not directly involved in nuclear activities, may also produce some radioactive wastes, e.g. radio-isotopes, chemical sludge etc.

  • E-wastes: Electronic wastes generated from any modern establishments. They may be described as discarded electrical or electronic devices. Some electronic scrap components, such as CRTs, may contain contaminants such as Pb, Cd, Be or brominated flame retardants.





(A) Waste to compost (i.e. resource recovery)

  • (A) Waste to compost (i.e. resource recovery)

  • Aerobic/Anaerobic composting

  • Vermicomposting – A major component of organic farming.



Energy can be recovered from the organic fraction of waste (bio-degradable as well as non bio-degradable) through two methods:

  • Energy can be recovered from the organic fraction of waste (bio-degradable as well as non bio-degradable) through two methods:

  • Thermo-chemical conversion: This process entails thermal decomposition of organic matter to produce either heat energy or fuel oil or gas.



Biochemical conversion: This process is based on enzymatic decomposition of organic matter by microbial action to produce methane gas or alcohol.

  • Biochemical conversion: This process is based on enzymatic decomposition of organic matter by microbial action to produce methane gas or alcohol.

  • Some of the important energy recovery techniques are discussed under the following heads:

  • Anaerobic digestion (AD):

  • Also known as bio-methanation

  • Segregating the organic fractions of waste



Feeding them into a closed container (biogas digester) under anaerobic condition

  • Feeding them into a closed container (biogas digester) under anaerobic condition

  • Organic wastes undergone bio-degradation and produce methane rich biogas and effluent/ sludge

  • Biogas produced, 50-150 m3/ton depending upon waste composition

  • Fundamentally, anaerobic digestion process can be divided into three stages with 3 distinct physiological groups of micro-organisms.



Stage I: Fermentative bacteria (anaerobic & facultative micro-organisms) e.g. Bacteroides succinogens, Clostridium sp.

  • Stage I: Fermentative bacteria (anaerobic & facultative micro-organisms) e.g. Bacteroides succinogens, Clostridium sp.

  • Complex organic materials, carbohydrates, proteins and lipids hydrolyzed & fermented into fatty acids, alcohol, CO2, H2, NH3 and sulfides.

  • Stage II: Acetogenic bacteria consume these primary products and produce H2, CO2 & acetic acid (CH3COOH). e.g. Syntrophobactor wolinii, Syntrophomonas wolfei



Stage III: Two types of methanogenic bacteria

  • Stage III: Two types of methanogenic bacteria

  • First one (reduces) CO2 to CH4 (e.g. Methanosprillium sp.)

  • Second one (decarboxylates) CH3COO- to CH4 (e.g. Methanosarcina sp.)



b) Incineration:

  • b) Incineration:

  • Direct burning of wastes in the presence of excess air (oxygen)

  • Liberates heat energy, inert gas and ash

  • About 65-80% of energy content of organic matter can be recovered



c) Pyrolysis:

  • c) Pyrolysis:

  • Also known as destructive distillation or carbonization

  • Thermal decomposition or organic matter at high temperature (about 900oC) in an inert (O2 deficient) atmosphere or vacuum.

  • Produces a mixture of combustible and non-combustible gases



c) Gasification:

  • c) Gasification:

  • Thermal decomposition of organic matter at high temperature in presence of limited amount of oxygen

  • Produces mainly a mixture of combustible & non-combustible gases

  • Temperature > 1000oC

  • The gas can be cooled, cleaned and utilized to generate electricity




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