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Principles of soil science

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Pabitra Mani

The document provides an overview of soil science, discussing the definition of soil, its layers (horizons), and various factors influencing soil formation. It highlights the significance of understanding soil properties for agricultural productivity and environmental management. Additionally, the text outlines the classification of different soil types and their characteristics in relation to agricultural practices.

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Soil-111 : Principles of Soil Science Dr. Pabitra Kumar Mani pabitramani@gmail.com www.bckv.edu.in www.slideshare.net.in/pabitramani Professor, Agril. Chemistry and Soil Science, F/Ag, BCKV
J N MukherjeeJustus von Liebig, 1840
What is Soil?What is Soil? Soil: Unconsolidated mineral or material on the surface of the earth resulting from and influenced by time, parent material, climate, organisms, and topography. Not all soil is created equal,Not all soil is created equal, ‘‘the soil’ vs. a soil.the soil’ vs. a soil. The soil is the link between the rock core of the earth and the living things on its surface. It is the foothold for the plants we grow. (Simonson,1957) Soil refers to the weathered and fragmented outer layer of the earth’s terrestrial surface. (Hillel, 1982)
Joffe (1949), modified by Birkeland(1999)
Soils Defined • Natural Body that Occurs on the Land Surface that are Characterized by One or More of the Following: – Consists of Distinct Horizons or Layers – The Ability to Support Rooted Plants in a Natural Environment – Upper Limit is Air or Shallow Water – Lower Limit is Bedrock or Limit of Biological Activity – Classification based on a typical depth of 2 m or approximately 6.0 feet
Principles of soil science
The pedosphere: abiotic and biotic entities interacting in the soil matrix
Principles of soil science
Better knowledge of the soils on which this road was built may have allowed its engineers to develop a more stable design, thus avoiding this costly and dangerous situation. (R. Weil)
Transcosna Grain Elevator, Canada (Oct. 18, 1913) Shear Failure under Foundation load
Branches of soil science
It deals with soil formation, soil genesis, soil classification and description of soil properties.  A pedologist studies, examines, and classifies soils as they occur in their natural environment. (from Gr. Pedos, “ground,” and logos, “science”; original formed as Russian, pedologiya)
A pedon is the smallest volume of soil that should be recognized as a soil individual The range of properties observed in several similar pedons, a polypedon are aggregated to define a soil individual.
A soil profile is a vertical cross section of a soil. It is divided into a number of distinct layers, referred to as horizons. The horizons are normally designated by symbols and letters. The presence or absence of particular horizons allows pedologists to classify the soil. In addition, the organic or O horizon can form above the mineral soil commonly in forested areas, resulting from the dead plant and animal remains. The basic unit of study: Soil Profiles TOPSOIL, upper or A horizon SUBSOIL, middle or B horizon PARENT MATERIAL, lower or C horizon
Information important to different soil functions and applications is most likely to be obtained by studying different layers of the soil profile.
The Regolith – What ? • The Regolith is the Unconsolidated material overlying Rock. The Overburden ! • This material may be rather thin to hundreds of feet thick and can include material dislodged or weathered from local rock, transported to the area by wind, water, ice, or gravity. Image Source: http:///soils.ag.uidaho.edu
The Soil or Solum • The Soil or Solum is the portion of the Regolith that has been influenced by the 5 Soil Formation Factors. • The processes are controlled by Time, Climate, Topography (Landform and Position), Organisms, and Parent Material. • Formation Process are in 4 Broad Categories (additions, losses, translocation, and transformations)- Genetic Soil Forming Processes.Rock – R Horizon SOIL Regolith
Young Soil Old Soil Well Defined Horizons High Degree of Weathering Highly Leached Thick Solum http://www.mo15.nrcs.usda.gov/features/gallery/ Poorly Defined Horizons Low Degree of Weathering Slightly Leached Thin Solum
Sediment Precipitation plus solutes, aerosols and particulates Organic residues  humus Primary  Secondary minerals minerals Leaching of dissolved ions & OM E(i)lluviation of clay CaCO3 dissolved ions dissolved OM Capillary rise of salts Capillary rise of dissolved ions Loss of gases N2 , N 2 O, CO2 Sediment Soil forming processes TRANSFORMATIONS Adapted from Stewart (1990) Additions Losses Losses Additions Additions TRANSLOCATIONS Losses TRANSLOCATIONS
C lim ateO rganism s R eliefParentm aterial Tim e H. Jenny refined the ideas of Russian scientist V.V. Dokuchaev into the following equation: 5 factors of soil formation Soil = f (Cl, O, R, P, T…)
Edaphology: Study of soil in relation to growth, nutrition and yield crops or plants. Edaphologists consider the various properties of soils in relation to plant production
Average Soil Composition { } Pore space 50% Solids 50% 25% Water 25% Air 5% Organic Matter 45% Inorganic (mineral materials)
Principles of soil science
Principles of soil science
Principles of soil science
Principles of soil science
Soil pH - a “master variable”Soil pH - a “master variable” Acid (pH=1.0) Neutral (pH=7.0) Alkaline (pH=14.0) • A measure of the hydrogen (H+ ) ion activity • One pH unit change = a ten fold change in acidity or alkalinity
Why called “master variable”?Why called “master variable”? • soil pH controls: 1) soil microbe activity 2) nutrient exchanges 3) nutrient availability 4) gaseous exchanges 5) chemical degradation 6) CEC
Possible pH Ranges Under Natural Soil Conditions black walnut: 6.0-8.0 Most desirable carrot: 5.5-7.0 cucumber: 5.5-7.0 spinach: 6.0-7.5 tomato: 5.5-7.5 white pine: 4.5-6.0 Very strong Strong Moderate Slight Slight Moderate Strong Very strong Neutral Acid Basic 3 4 5 6 7 8 9 10 111 2 12 13 14 Most agricultural soils Extreme pH range for most mineral soils cranberry:4.2-5.0 apple: 5.0-6.5
Soil pH 0 100 4.0 5.0 6.0 7.0 8.0 Plant benefit Plant Injury Toxicity Deficiency Relativeplantyield(%) (Weil and Kroontje,1984) General relationship of plant health and soil pH. Some nutrients can reach toxic levels at low pHs, while deficiencies can occur at high pHs.
Soren P.L. Sorensen invented the pH scale in 1909.
Principles of soil science
Principles of soil science
[ ][ ] [ ]HAca K −+ = AcH [ ] [ ] [ ]- Ac H HAcKa =+ [ ]HAc Aclog a pKpH     − +=∴ This form of ionisation constant equation is called the Henderson- Hasselbalch equation. pH of an weak acid [ ]     −     += AcHHAc
Principles of soil science
pH meter When one metal is brought in contact with another, a voltage difference occurs due to their differences in electron mobility.  When a metal is brought in contact with a solution of salts or acids, a similar electric potential is caused, which has led to the invention of batteries.  Similarly, an electric potential develops when one liquid is brought in contact with another one, but a membrane is needed to keep such liquids apart. A pH meter measures essentially the electro-chemical potential between a known liquid inside the glass electrode (membrane) and an unknown liquid outside. Because the thin glass bulb allows mainly the agile and small hydrogen ions to interact with the glass, the glass electrode measures the electro-chemical potential of hydrogen ions or the potential of hydrogen. To complete the electrical circuit, also a reference electrode is needed. Note that the instrument does not measure a current but only an electrical voltage, yet a small leakage of ions from the reference electrode is needed, forming a conducting bridge to the glass electrode.
The majority of pH electrodes available commercially are combination electrodes that have both glass H+ ion sensitive electrode and  additional reference electrode conveniently placed in one housing.
In principle it should be possible to determine the H+ ion activity or concn. of a soln by measuring the potential of a Hydrogen electrode inserted in the given soln. The EMF of a cell, free from liquid junction potential, consisting of a Hydrogen electrode and a reference electrode, should be given by, E = E ref – RT/F ln aH+ F= Faraday constant ,96,485 E = E ref + 2.303 RT/F pH R= 8.314 J/mol/°K ∴pH = ( E- Eref )F/2.303 RT T= Kelvin scale So, by measuring the EMF of the Cell E obtained by combining the H electrode with a reference electrode of known potential, Eref , the pH of the soln. may be evaluated. The electric potential at any point is defined as the work done in bringing a unit charge from infinity to the particular point Reduced state Oxidised state + n Electron⇋ M = Mn+ + nE E(+) = E0 – (RT/F) ln aM n+ Nernst Equation Principles of pH Meter
Soil pH & Nutrient Availability
Principles of soil science
Principles of soil science
Factors Influencing pH Organic Matter Soil Parent Material (carbonates, etc.) Temperature and Precipitation Agricultural Practices Organic matter affects the buffering capacity of the soil (more SOM-resistance to change pH) Soil parent materials such as basalt have higher pH levels than those of parent materials from granite. High temperature and moisture leach bases from soil . Agricultural practices tend to lower pHAgricultural practices tend to lower pH •crops removing nutrients • leaching nutrients through soil; •decomposition of organic materials; • fertilization, particularly ammonium fertilizers; •Liming materials raise soil pH
Principles of soil science
Soil Fertility: it is the potential of the earth or inherent capacity of the soil to supply plant nutrients in quantity, forms and proportion required for the growth and development of the crop. Fertility is measured by the amount of chemical elements or compounds required for plant growth Productivity of a soil is defined as its capacity to produce plants under specified programme of management. It is measured by the yield of the crop per unit area of the land Fertility is one of the factors of soil productivity. Sometimes a soil may be fertile but may not be productive.
Types of soils Alluvial Soil Black Soil Mountain Soil Desert soil Red soil Laterite Soil
Alluvial Soil This is the most wide spread soil in india.This soil is formed by the deposition of materials by the rivers namely Indus,the Ganga, the Brahmputra. It is mainly found in Northern Plains and Eastern Coastal Plains. It is the most fertile soil. Due to high fertility, they are intensively cultivated and are densely populated.
Black Soil This soil is black in colour and is best for growing cotton and sugarcane. This soil is formed by the weathering up of igneous rocks.It is rich in minerals like iron and magnesium. It is mainly confined to the north western part of peninsular plateau, Deccan lava plateau which includes the states of Maharashtra, Saurashtra, Malwa, Madhya Pradesh and Chhattisgarh.
Laterite Soil These soils are formed by the intense leaching in tropical regions where the rainfall is high. This soil is devoid of nutrients and has low humus content and is not suitable for crop cultivation. It is mainly found in Karnatka, Kerala, TamilNadu,Madhya Pradesh and hilly areas of Orissa and Assam. Through soil conservation techniques they are useful for growing tea and coffee.
Desert Arid Soils These are sandy,porous and saline in nature. They lack humus and moisture. Hence they are not suitable for cultivation except in areas where irrigation is available. This soil is mainly found in Rajasthan and some parts of Gujarat.
Red Soil Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and south eastern parts of the Deccan Plateau. This soil is rich in iron compounds and is reddish in colour while it is yellowish in colour when it occurs in hydrated form.
Principles of soil science
Pedon.—The pedon is presented in Soil Taxonomy (Soil Survey Staff, 1975) as a unit of sampling within a soil. The limits on the area of a pedon establish rules for deciding whethe consider one or two or more kinds of soil within a small-scale pattern of local lateral variabi A pedon is regarded as the smallest body of one kind of soil large enough to represent the nature and arrangement of horizons and variability in the other properties that are preserve samples. A pedon extends down to the lower limit of a soil. It extends through all genetic horizons an the genetic horizons are thin, into the upper part of the underlying material. The pedon includes the rooting zone of most native perennial plants. For purposes of most soil survey practical lower limit of the pedon is bedrock or a depth of about 2 m, whichever is shallowe depth of 2 m provides a good sample of major soil horizons, even in thick soil. It includes m of the volume of soil penetrated by plant roots, and it permits reliable observations of soil properties. The surface of a pedon is roughly polygonal and ranges from 1 m2 to 10 m2 in area, depending on the nature of the variability in the soil. Where the cycle of variations is less th 2 m and all horizons are continuous and nearly uniform in thickness, the pedon has an are approximately 1 m2. Where horizons or other properties are intermittent or cyclic over an interval of 2 to 7 m, the pedon includes one-half of the cycle (1 to 3 1/2 m). If horizons are cyclic over an interval greater than 7 m, each cycle is considered to contain more than one soil. The range in size, 1 to 10 m2, permits consistent classification by different observers where important horizons are cyclic or repeatedly interrupted over short distances. Polypedon.—The pedon is considered too small to exhibit more extensive features, such
Principles of soil science
Bulk Density DeterminationBulk Density Determination For our example, let’s assume we have 1 cubic centimeter of soil that weighs 1.33 grams Soil is made of solids and pore spaces 1.33 grams To calculate Bulk Density: Volume = 1 cm3 Weight = 1.33 grams Bulk Density = Weight of Soil Volume of Soil Bulk Density = 1.33 1 Bulk Density = 1.33 grams/cm3 { }
Porosity value generally ranges from 0.3 to 0.6 (30– 60%). In clayey soils, the porosity is highly variable because the soi alternately swells, shrinks, aggregates, disperses, compacts, and cracks it ranges between 0.3 and 2.
Comparison of Coarse Textured and Fine Textured Soils Coarse Textured Soil Less porespace but more macropores Fine Textured Soil More total porespace Texture and Pore SpaceTexture and Pore Space
Clay Silty Clay Silty Clay Loam Clay Loam Sandy Clay Sandy Clay Loam Loam Silt Loam Silt Sandy Loam Sand Percent Clay Percent Silt Percent Sand Fine Medium Coarse Loamy Sand
Soil StructureSoil Structure • Soil structure is the combination or arrangement of primary soil particles into secondary units • The way soil particles are arranged to form stable aggregates • Compare this to clods, which are caused by disturbance (plowing or digging) • Compaction – results from implement traffic, stable soil aggregates are broken down
Common Types of SoilCommon Types of Soil StructureStructure Common to Ohio soils just below Ap (> 8”) Plow layer Sand Deeper in profile (>3-4’) Granular Platy Prismatic Columnar Blocky Single Grain Massive
GRANULAR
BLOCKY
C B E A Granular Platy Blocky Massive
. . . more on Soil Horizons. . . more on Soil Horizons Mollisol Alfisol B C Ap A
Soil Horizons A black Leaching zone: roots here (topsoil) B “red” Accumulating zone: nutrients (subsoil) C rocky Weathered bedrock D solid Bedrock Horizons subject to erosion Black color is caused by organic particles Prevented by: • Mulching • Proper cultivation • Perennial planting Rotting material makes humus particles • Improve drainage (air capacity) • Increase water holding capacity • Increase nutrient holding capacity leaves, grass clippings, compost, green manure, horse
Typical electrode system for measuring pH. (a) Glass electrode (indicator) and saturated calomel electrode (reference) immersed in a solution of unknown pH. (b) Combination probe consisting of both an indicator glass electrode and a silver/silver chloride reference. A second silver/silver chloride electrode serves as the internal reference for the glass electrode. The two electrodes are arranged concentrically with the internal reference in the center and the external reference outside. The reference makes contact with the analyte solution through the glass frit or other suitable porous medium. Combination probes are the most common configuration of glass electrode and reference for measuring pH.
Soil is a natural body consisting of layers (horizons) of mineral and/or organic constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical properties and their biological characteristics.
Built entirely from natural, locally occurring materials, this typical rural Tanzanian house has soil walls made by daubing mud onto a framework of sticks. Both its soil walls and grass thatch roof are shown in the process of being refurbished. For scale, note man standing left of the house. (Photo courtesy of R. Weil)
68 Shear Strength of Soils Dr. Attaullah Shah Shear strength of a soil is the resistance to deformation by continuous shear displacement of soil particles due to tangential (shear) stress.
Climate and Soil Development Image Source: University of Wisconsin, 2002
Principles of soil science
Principles of soil science
Soil Development
There are 5 main factors that influenceThere are 5 main factors that influence soil formation processes.soil formation processes. 1. Type of Parent Material1. Type of Parent Material 2. Climate2. Climate 3. Topography3. Topography 4. Biotic Components4. Biotic Components 5. Time5. Time
Soil ProfileSoil Profile What do we see? • organic matter - surface soil isorganic matter - surface soil is darker due to organic matterdarker due to organic matter • iron oxides - subsoil hasiron oxides - subsoil has brighter browns and tans duebrighter browns and tans due to iron oxidesto iron oxides • drainagedrainage • horizons - layers of differenthorizons - layers of different color or texture; formed fromcolor or texture; formed from the top downthe top down
Soil Quality Indicators Physical Chemical Biological Organic Matter Chemical Physical Biological OM
Physical Soil Quality Indicators Soil Structure Aggregate Stability Bulk Density/Compaction Soil Pores Permeability Infiltration Surface Crusting Available Water Holding Capacity
Chemical Soil Quality Indicators Soil pH Nutrient Supply Potentially Mineralizable Nitrogen Cation Exchange Capacity Calcium Carbonate Salinity and Sodicity – Electrical Conductivity – Exchangeable Sodium Percentage Soil Contaminants
Biological Soil Quality Indicators The “Big Picture:” the Soil Food Web Indicators –Microbial Biomass –Soil Enzymes –Soil Respiration –Plant Roots –Other Indicators
Soil Organic Matter  Considered the single most importantConsidered the single most important indicator of soil qualityindicator of soil quality Organic matter - Critical in soils since it contributes to infiltration, AWC, CEC, soil structure, and provides energy source for microorganisms, which are important in decomposition of OM and release of nutrients needed for crops and overall plant growth and aggregation of soils. Because OM is important to CEC as is clay; OM becomes very important in sandy soils since they are inherently low in clay
Principles of soil science
Pedon:: PedPed - Ground,- Ground, LogosLogos - Discourse/ Science- Discourse/ Science Pedology-- The scienceThe science that deals with formation,that deals with formation, morphology and classification of soilmorphology and classification of soil bodies as land scape componentbodies as land scape component Pedogenesis--The natural process of soil FormationThe natural process of soil Formation WeatheringWeathering Rock --------------Parent Material 1. Physical 2. Chemical 3. Biological
Pedogenic Processes: Pedogenic processes are Parent Material Soil extremely complex involving many physical, chemical & biological reactions Different processes or their combinations Parent Material Soils (Same type) depends on variation in natural environment of different nature Parent Material Effect of same natural Soils Different types Environment of different nature This is the material from which the soil has developed and can vary from solid rock to deposits like alluvium and boulder clay. It has been defined as ‘the initial state of the soil system’.

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Principles of soil science

  • 1. Soil-111 : Principles of Soil Science Dr. Pabitra Kumar Mani pabitramani@gmail.com www.bckv.edu.in www.slideshare.net.in/pabitramani Professor, Agril. Chemistry and Soil Science, F/Ag, BCKV
  • 2. J N MukherjeeJustus von Liebig, 1840
  • 3. What is Soil?What is Soil? Soil: Unconsolidated mineral or material on the surface of the earth resulting from and influenced by time, parent material, climate, organisms, and topography. Not all soil is created equal,Not all soil is created equal, ‘‘the soil’ vs. a soil.the soil’ vs. a soil. The soil is the link between the rock core of the earth and the living things on its surface. It is the foothold for the plants we grow. (Simonson,1957) Soil refers to the weathered and fragmented outer layer of the earth’s terrestrial surface. (Hillel, 1982)
  • 4. Joffe (1949), modified by Birkeland(1999)
  • 5. Soils Defined • Natural Body that Occurs on the Land Surface that are Characterized by One or More of the Following: – Consists of Distinct Horizons or Layers – The Ability to Support Rooted Plants in a Natural Environment – Upper Limit is Air or Shallow Water – Lower Limit is Bedrock or Limit of Biological Activity – Classification based on a typical depth of 2 m or approximately 6.0 feet
  • 7. The pedosphere: abiotic and biotic entities interacting in the soil matrix
  • 9. Better knowledge of the soils on which this road was built may have allowed its engineers to develop a more stable design, thus avoiding this costly and dangerous situation. (R. Weil)
  • 10. Transcosna Grain Elevator, Canada (Oct. 18, 1913) Shear Failure under Foundation load
  • 11. Branches of soil science
  • 12. It deals with soil formation, soil genesis, soil classification and description of soil properties.  A pedologist studies, examines, and classifies soils as they occur in their natural environment. (from Gr. Pedos, “ground,” and logos, “science”; original formed as Russian, pedologiya)
  • 13. A pedon is the smallest volume of soil that should be recognized as a soil individual The range of properties observed in several similar pedons, a polypedon are aggregated to define a soil individual.
  • 14. A soil profile is a vertical cross section of a soil. It is divided into a number of distinct layers, referred to as horizons. The horizons are normally designated by symbols and letters. The presence or absence of particular horizons allows pedologists to classify the soil. In addition, the organic or O horizon can form above the mineral soil commonly in forested areas, resulting from the dead plant and animal remains. The basic unit of study: Soil Profiles TOPSOIL, upper or A horizon SUBSOIL, middle or B horizon PARENT MATERIAL, lower or C horizon
  • 15. Information important to different soil functions and applications is most likely to be obtained by studying different layers of the soil profile.
  • 16. The Regolith – What ? • The Regolith is the Unconsolidated material overlying Rock. The Overburden ! • This material may be rather thin to hundreds of feet thick and can include material dislodged or weathered from local rock, transported to the area by wind, water, ice, or gravity. Image Source: http:///soils.ag.uidaho.edu
  • 17. The Soil or Solum • The Soil or Solum is the portion of the Regolith that has been influenced by the 5 Soil Formation Factors. • The processes are controlled by Time, Climate, Topography (Landform and Position), Organisms, and Parent Material. • Formation Process are in 4 Broad Categories (additions, losses, translocation, and transformations)- Genetic Soil Forming Processes.Rock – R Horizon SOIL Regolith
  • 18. Young Soil Old Soil Well Defined Horizons High Degree of Weathering Highly Leached Thick Solum http://www.mo15.nrcs.usda.gov/features/gallery/ Poorly Defined Horizons Low Degree of Weathering Slightly Leached Thin Solum
  • 19. Sediment Precipitation plus solutes, aerosols and particulates Organic residues  humus Primary  Secondary minerals minerals Leaching of dissolved ions & OM E(i)lluviation of clay CaCO3 dissolved ions dissolved OM Capillary rise of salts Capillary rise of dissolved ions Loss of gases N2 , N 2 O, CO2 Sediment Soil forming processes TRANSFORMATIONS Adapted from Stewart (1990) Additions Losses Losses Additions Additions TRANSLOCATIONS Losses TRANSLOCATIONS
  • 20. C lim ateO rganism s R eliefParentm aterial Tim e H. Jenny refined the ideas of Russian scientist V.V. Dokuchaev into the following equation: 5 factors of soil formation Soil = f (Cl, O, R, P, T…)
  • 21. Edaphology: Study of soil in relation to growth, nutrition and yield crops or plants. Edaphologists consider the various properties of soils in relation to plant production
  • 22. Average Soil Composition { } Pore space 50% Solids 50% 25% Water 25% Air 5% Organic Matter 45% Inorganic (mineral materials)
  • 27. Soil pH - a “master variable”Soil pH - a “master variable” Acid (pH=1.0) Neutral (pH=7.0) Alkaline (pH=14.0) • A measure of the hydrogen (H+ ) ion activity • One pH unit change = a ten fold change in acidity or alkalinity
  • 28. Why called “master variable”?Why called “master variable”? • soil pH controls: 1) soil microbe activity 2) nutrient exchanges 3) nutrient availability 4) gaseous exchanges 5) chemical degradation 6) CEC
  • 29. Possible pH Ranges Under Natural Soil Conditions black walnut: 6.0-8.0 Most desirable carrot: 5.5-7.0 cucumber: 5.5-7.0 spinach: 6.0-7.5 tomato: 5.5-7.5 white pine: 4.5-6.0 Very strong Strong Moderate Slight Slight Moderate Strong Very strong Neutral Acid Basic 3 4 5 6 7 8 9 10 111 2 12 13 14 Most agricultural soils Extreme pH range for most mineral soils cranberry:4.2-5.0 apple: 5.0-6.5
  • 30. Soil pH 0 100 4.0 5.0 6.0 7.0 8.0 Plant benefit Plant Injury Toxicity Deficiency Relativeplantyield(%) (Weil and Kroontje,1984) General relationship of plant health and soil pH. Some nutrients can reach toxic levels at low pHs, while deficiencies can occur at high pHs.
  • 31. Soren P.L. Sorensen invented the pH scale in 1909.
  • 34. [ ][ ] [ ]HAca K −+ = AcH [ ] [ ] [ ]- Ac H HAcKa =+ [ ]HAc Aclog a pKpH     − +=∴ This form of ionisation constant equation is called the Henderson- Hasselbalch equation. pH of an weak acid [ ]     −     += AcHHAc
  • 36. pH meter When one metal is brought in contact with another, a voltage difference occurs due to their differences in electron mobility.  When a metal is brought in contact with a solution of salts or acids, a similar electric potential is caused, which has led to the invention of batteries.  Similarly, an electric potential develops when one liquid is brought in contact with another one, but a membrane is needed to keep such liquids apart. A pH meter measures essentially the electro-chemical potential between a known liquid inside the glass electrode (membrane) and an unknown liquid outside. Because the thin glass bulb allows mainly the agile and small hydrogen ions to interact with the glass, the glass electrode measures the electro-chemical potential of hydrogen ions or the potential of hydrogen. To complete the electrical circuit, also a reference electrode is needed. Note that the instrument does not measure a current but only an electrical voltage, yet a small leakage of ions from the reference electrode is needed, forming a conducting bridge to the glass electrode.
  • 37. The majority of pH electrodes available commercially are combination electrodes that have both glass H+ ion sensitive electrode and  additional reference electrode conveniently placed in one housing.
  • 38. In principle it should be possible to determine the H+ ion activity or concn. of a soln by measuring the potential of a Hydrogen electrode inserted in the given soln. The EMF of a cell, free from liquid junction potential, consisting of a Hydrogen electrode and a reference electrode, should be given by, E = E ref – RT/F ln aH+ F= Faraday constant ,96,485 E = E ref + 2.303 RT/F pH R= 8.314 J/mol/°K ∴pH = ( E- Eref )F/2.303 RT T= Kelvin scale So, by measuring the EMF of the Cell E obtained by combining the H electrode with a reference electrode of known potential, Eref , the pH of the soln. may be evaluated. The electric potential at any point is defined as the work done in bringing a unit charge from infinity to the particular point Reduced state Oxidised state + n Electron⇋ M = Mn+ + nE E(+) = E0 – (RT/F) ln aM n+ Nernst Equation Principles of pH Meter
  • 39. Soil pH & Nutrient Availability
  • 42. Factors Influencing pH Organic Matter Soil Parent Material (carbonates, etc.) Temperature and Precipitation Agricultural Practices Organic matter affects the buffering capacity of the soil (more SOM-resistance to change pH) Soil parent materials such as basalt have higher pH levels than those of parent materials from granite. High temperature and moisture leach bases from soil . Agricultural practices tend to lower pHAgricultural practices tend to lower pH •crops removing nutrients • leaching nutrients through soil; •decomposition of organic materials; • fertilization, particularly ammonium fertilizers; •Liming materials raise soil pH
  • 44. Soil Fertility: it is the potential of the earth or inherent capacity of the soil to supply plant nutrients in quantity, forms and proportion required for the growth and development of the crop. Fertility is measured by the amount of chemical elements or compounds required for plant growth Productivity of a soil is defined as its capacity to produce plants under specified programme of management. It is measured by the yield of the crop per unit area of the land Fertility is one of the factors of soil productivity. Sometimes a soil may be fertile but may not be productive.
  • 45. Types of soils Alluvial Soil Black Soil Mountain Soil Desert soil Red soil Laterite Soil
  • 46. Alluvial Soil This is the most wide spread soil in india.This soil is formed by the deposition of materials by the rivers namely Indus,the Ganga, the Brahmputra. It is mainly found in Northern Plains and Eastern Coastal Plains. It is the most fertile soil. Due to high fertility, they are intensively cultivated and are densely populated.
  • 47. Black Soil This soil is black in colour and is best for growing cotton and sugarcane. This soil is formed by the weathering up of igneous rocks.It is rich in minerals like iron and magnesium. It is mainly confined to the north western part of peninsular plateau, Deccan lava plateau which includes the states of Maharashtra, Saurashtra, Malwa, Madhya Pradesh and Chhattisgarh.
  • 48. Laterite Soil These soils are formed by the intense leaching in tropical regions where the rainfall is high. This soil is devoid of nutrients and has low humus content and is not suitable for crop cultivation. It is mainly found in Karnatka, Kerala, TamilNadu,Madhya Pradesh and hilly areas of Orissa and Assam. Through soil conservation techniques they are useful for growing tea and coffee.
  • 49. Desert Arid Soils These are sandy,porous and saline in nature. They lack humus and moisture. Hence they are not suitable for cultivation except in areas where irrigation is available. This soil is mainly found in Rajasthan and some parts of Gujarat.
  • 50. Red Soil Red soil develops on crystalline igneous rocks in areas of low rainfall in the eastern and south eastern parts of the Deccan Plateau. This soil is rich in iron compounds and is reddish in colour while it is yellowish in colour when it occurs in hydrated form.
  • 52. Pedon.—The pedon is presented in Soil Taxonomy (Soil Survey Staff, 1975) as a unit of sampling within a soil. The limits on the area of a pedon establish rules for deciding whethe consider one or two or more kinds of soil within a small-scale pattern of local lateral variabi A pedon is regarded as the smallest body of one kind of soil large enough to represent the nature and arrangement of horizons and variability in the other properties that are preserve samples. A pedon extends down to the lower limit of a soil. It extends through all genetic horizons an the genetic horizons are thin, into the upper part of the underlying material. The pedon includes the rooting zone of most native perennial plants. For purposes of most soil survey practical lower limit of the pedon is bedrock or a depth of about 2 m, whichever is shallowe depth of 2 m provides a good sample of major soil horizons, even in thick soil. It includes m of the volume of soil penetrated by plant roots, and it permits reliable observations of soil properties. The surface of a pedon is roughly polygonal and ranges from 1 m2 to 10 m2 in area, depending on the nature of the variability in the soil. Where the cycle of variations is less th 2 m and all horizons are continuous and nearly uniform in thickness, the pedon has an are approximately 1 m2. Where horizons or other properties are intermittent or cyclic over an interval of 2 to 7 m, the pedon includes one-half of the cycle (1 to 3 1/2 m). If horizons are cyclic over an interval greater than 7 m, each cycle is considered to contain more than one soil. The range in size, 1 to 10 m2, permits consistent classification by different observers where important horizons are cyclic or repeatedly interrupted over short distances. Polypedon.—The pedon is considered too small to exhibit more extensive features, such
  • 54. Bulk Density DeterminationBulk Density Determination For our example, let’s assume we have 1 cubic centimeter of soil that weighs 1.33 grams Soil is made of solids and pore spaces 1.33 grams To calculate Bulk Density: Volume = 1 cm3 Weight = 1.33 grams Bulk Density = Weight of Soil Volume of Soil Bulk Density = 1.33 1 Bulk Density = 1.33 grams/cm3 { }
  • 55. Porosity value generally ranges from 0.3 to 0.6 (30– 60%). In clayey soils, the porosity is highly variable because the soi alternately swells, shrinks, aggregates, disperses, compacts, and cracks it ranges between 0.3 and 2.
  • 56. Comparison of Coarse Textured and Fine Textured Soils Coarse Textured Soil Less porespace but more macropores Fine Textured Soil More total porespace Texture and Pore SpaceTexture and Pore Space
  • 57. Clay Silty Clay Silty Clay Loam Clay Loam Sandy Clay Sandy Clay Loam Loam Silt Loam Silt Sandy Loam Sand Percent Clay Percent Silt Percent Sand Fine Medium Coarse Loamy Sand
  • 58. Soil StructureSoil Structure • Soil structure is the combination or arrangement of primary soil particles into secondary units • The way soil particles are arranged to form stable aggregates • Compare this to clods, which are caused by disturbance (plowing or digging) • Compaction – results from implement traffic, stable soil aggregates are broken down
  • 59. Common Types of SoilCommon Types of Soil StructureStructure Common to Ohio soils just below Ap (> 8”) Plow layer Sand Deeper in profile (>3-4’) Granular Platy Prismatic Columnar Blocky Single Grain Massive
  • 63. . . . more on Soil Horizons. . . more on Soil Horizons Mollisol Alfisol B C Ap A
  • 64. Soil Horizons A black Leaching zone: roots here (topsoil) B “red” Accumulating zone: nutrients (subsoil) C rocky Weathered bedrock D solid Bedrock Horizons subject to erosion Black color is caused by organic particles Prevented by: • Mulching • Proper cultivation • Perennial planting Rotting material makes humus particles • Improve drainage (air capacity) • Increase water holding capacity • Increase nutrient holding capacity leaves, grass clippings, compost, green manure, horse
  • 65. Typical electrode system for measuring pH. (a) Glass electrode (indicator) and saturated calomel electrode (reference) immersed in a solution of unknown pH. (b) Combination probe consisting of both an indicator glass electrode and a silver/silver chloride reference. A second silver/silver chloride electrode serves as the internal reference for the glass electrode. The two electrodes are arranged concentrically with the internal reference in the center and the external reference outside. The reference makes contact with the analyte solution through the glass frit or other suitable porous medium. Combination probes are the most common configuration of glass electrode and reference for measuring pH.
  • 66. Soil is a natural body consisting of layers (horizons) of mineral and/or organic constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical properties and their biological characteristics.
  • 67. Built entirely from natural, locally occurring materials, this typical rural Tanzanian house has soil walls made by daubing mud onto a framework of sticks. Both its soil walls and grass thatch roof are shown in the process of being refurbished. For scale, note man standing left of the house. (Photo courtesy of R. Weil)
  • 68. 68 Shear Strength of Soils Dr. Attaullah Shah Shear strength of a soil is the resistance to deformation by continuous shear displacement of soil particles due to tangential (shear) stress.
  • 69. Climate and Soil Development Image Source: University of Wisconsin, 2002
  • 73. There are 5 main factors that influenceThere are 5 main factors that influence soil formation processes.soil formation processes. 1. Type of Parent Material1. Type of Parent Material 2. Climate2. Climate 3. Topography3. Topography 4. Biotic Components4. Biotic Components 5. Time5. Time
  • 74. Soil ProfileSoil Profile What do we see? • organic matter - surface soil isorganic matter - surface soil is darker due to organic matterdarker due to organic matter • iron oxides - subsoil hasiron oxides - subsoil has brighter browns and tans duebrighter browns and tans due to iron oxidesto iron oxides • drainagedrainage • horizons - layers of differenthorizons - layers of different color or texture; formed fromcolor or texture; formed from the top downthe top down
  • 75. Soil Quality Indicators Physical Chemical Biological Organic Matter Chemical Physical Biological OM
  • 76. Physical Soil Quality Indicators Soil Structure Aggregate Stability Bulk Density/Compaction Soil Pores Permeability Infiltration Surface Crusting Available Water Holding Capacity
  • 77. Chemical Soil Quality Indicators Soil pH Nutrient Supply Potentially Mineralizable Nitrogen Cation Exchange Capacity Calcium Carbonate Salinity and Sodicity – Electrical Conductivity – Exchangeable Sodium Percentage Soil Contaminants
  • 78. Biological Soil Quality Indicators The “Big Picture:” the Soil Food Web Indicators –Microbial Biomass –Soil Enzymes –Soil Respiration –Plant Roots –Other Indicators
  • 79. Soil Organic Matter  Considered the single most importantConsidered the single most important indicator of soil qualityindicator of soil quality Organic matter - Critical in soils since it contributes to infiltration, AWC, CEC, soil structure, and provides energy source for microorganisms, which are important in decomposition of OM and release of nutrients needed for crops and overall plant growth and aggregation of soils. Because OM is important to CEC as is clay; OM becomes very important in sandy soils since they are inherently low in clay
  • 81. Pedon:: PedPed - Ground,- Ground, LogosLogos - Discourse/ Science- Discourse/ Science Pedology-- The scienceThe science that deals with formation,that deals with formation, morphology and classification of soilmorphology and classification of soil bodies as land scape componentbodies as land scape component Pedogenesis--The natural process of soil FormationThe natural process of soil Formation WeatheringWeathering Rock --------------Parent Material 1. Physical 2. Chemical 3. Biological
  • 82. Pedogenic Processes: Pedogenic processes are Parent Material Soil extremely complex involving many physical, chemical & biological reactions Different processes or their combinations Parent Material Soils (Same type) depends on variation in natural environment of different nature Parent Material Effect of same natural Soils Different types Environment of different nature This is the material from which the soil has developed and can vary from solid rock to deposits like alluvium and boulder clay. It has been defined as ‘the initial state of the soil system’.

Editor's Notes

  • #4: The soil vs. a soil- If "the soil" is thought of like a forest, "a soil" would be an individual tree in that forest. The same applies to soil.
  • #23: An average soil is composed of mineral matter, organic matter, and pore space, which may be occupied by air and/or water. The percentage of these four components can vary depending on how and where the soils were formed. 50% solids and 50% pore space; obviously, these are mixed in a natural environment and fluctuate greatly throughout the year.
  • #28: Soil pH is a measure of the hydrogen ion activity and is expressed on a scale of 1 to 14. Soil pH can sometimes be confusing the way it is expressed. Many growers associate a one unit change in pH with very little change in soil acidity. They fail to recognize that soil pH is expressed on a logarithmic scale, and that a one unit change in pH is actually a 10X change in hydrogen ion concentration.
  • #31: General relationship of plant health and soil pH. Some nutrients can reach toxic levels at low pHs, while deficiencies can occur at high pHs.
  • #43: Organic matter affects the buffering capacity of the soil (more SOM-resistance to change pH) Soil parent materials such as basalt have higher pH levels than those of parent materials from granite. High temperature and moisture leach bases from soil (NW to SE tends to have more acid soils). Agricultural practices tend to lower pH crops removing nutrients leaching nutrients through soil decomposition of organic materials fertilization, particularly ammonium fertilizers Liming materials raise soil pH (refer to Agronomy Technical Note No. 8 on Liming).
  • #55: Bulk density is simply dry weight of soil divided by total volume of soil.
  • #57: Soils with a high proportion of pore space to solids have lower bulk densities than those that are more compact and have less pore space. Sandy soils have bulk densities that are commonly higher than in the finer-textured soils such as clay loams and clays. This fact may seem counterintuitive at first because sandy soils are commonly referred to as ‘light’ soils, while clays are commonly referred to as ‘heavy’ soils. In this case, ‘light’ and ‘heavy’ do not refer to bulk density, but rather the amount of effort required for tillage.
  • #58: There are 12 basic textural classes found on the texture triangle. Each class can determine fertility, ease of tillage, droughtiness, and general productivity. There are two widely acceptable ways to determine soil texture. The first is determining texture by feel. The second method requires some laboratory equipment, and is referred to the hydrometer method. The hydrometer method separates particles by their rate of settling in water. The texture of a soil can be found by knowing (or estimating) the percentage of two of the three components, usually clay and sand in the hydrometer method.
  • #60: There are many different types of soil structure, but the most common are granular, platy, blocky, prismatic, and massive. Granular is normally found in the A horizon. Platy is sometimes found at the base of the A horizon, or near the top of the B horizon. Blocky and prismatic are most common in the B horizon and massive is usually associated with the C horizon. A common question to consider for agricultural interests is ‘How is structure formed?’ The largest component is microbial exudates. Therefore, additions of organic matter from residue or manure will in theory lead to formation of stable peds. Granular, platy, prismatic, columnar, and block are all generically referred to as peds. Single grain and massive are understood to be structureless.
  • #64: Mollisols: *characterized by a thick, dark profile *predominant soils under grassland or prairie native vegetation *considered to be some of the most naturally fertile soils in the world *~25% of land in the U.S. is classified as mollisol (most in the world) *mollisols are dominant Illinois and Iowa; but they also dominate northern Argentina and southern Brazil. *the former USSR has vast amounts of soil classified as mollisols Alfisols: *characterized by an argillic (overlaying layer has deposited clays) Bt horizon *~14% of soils in the U.S. are classified as alfisols *dominates Ohio
  • #76: Soils have chemical, biological, and physical properties that interact in a complex way to give a soil its quality or capacity to function. An indicator is an indirect measure of soil quality or soil function. They are not measures of soil quality, but collectively tell us whether the soil is functioning normally. Physical properties - infiltration, structure, aggregate stability, porosity, and bulk density. Chemical properties - salinity, soil pH, cation exchange capacity, plant nutrients, organic matter content, etc. Biological properties - earthworm numbers, and other animal activities that are important in soil development and fertility, soil respiration, pitfall trapping, microbial biomass, cotton strip assay, soil food web structure, etc. Organic Matter (OM) has physical, chemical, and biological properties. It is considered part of all three groups.
  • #77: List of most commonly used physical soil quality indicators. Each will be covered in detail the slides to follow. All of these indicators are interrelated. What affects one, or by changing one, could affect one or more of the others. As individual indicators are discussed you will see this interaction. Last 4 specific to water movement. All important for root growth, aeration, erosion protection.
  • #78: List of chemical indicators that will be covered in more detail in this section. Organized by general category: Optimize pH, nutrients Maximize CEC (OM) Minimize CaCO3, Na, contaminants
  • #79: The importance of soil biology has long been recognized. Biological systems are highly sensitive and a change in the biological status of the soil may provide us with an early warning of potential environmental damage. The balance of the entire community perform many functions that affect agroecosystem health. But this web of complex interactions is very difficult to measure directly. Recently sophisticated methods of assessment been developed. However, in many cases their interpretation remains problematic. Other indicators: Cotton strip assay Arthropod Pitfall trapping Microbial quotient--microbial biomass divided by the soil respiration rate
  • #80: Organic matter - Critical in soils since it contributes to infiltration, AWC, CEC, soil structure, and provides energy source for microorganisms, which are important in decomposition of OM and release of nutrients needed for crops and overall plant growth and aggregation of soils. Because OM is important to CEC as is clay; OM becomes very important in sandy soils since they are inherently low in clay. Hence, CEC in sandy soils may come almost entirely from the OM content.