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Soil physics atterberg limit,compaction, shear strength,crusting and puddling


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Soil mechanics including Atterbergs limit, shear strength, compaction, crusting , puddling , tilth index etc.P K MANI

Soil mechanics including Atterbergs limit, shear strength, compaction, crusting , puddling , tilth index etc.P K MANI

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  • 1. Soil Physics ACSS-501 Dr. P.K. Mani Department of Agril. Chemistry and Soil Science Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India E-mail:, Website: Copyright© Markus Tuller and Dani Or2002-2004
  • 2. Syllabus: Unit-III: Soil consistence, Dispersion and workability of soils; Soil Compaction and consolidation; Soil strength, swelling and shrinkage-basic concepts Unit-IV: Soil tilth, characteristics of good soil tilth; Soil crusting-mechanism, factors affecting and evaluation; Soil conditioners, Puddling, its effect on soil physical properties; Clod formation. Copyright© Markus Tuller and Dani Or2002-2004
  • 3. Daniel Hillel has written the most widely used textbooks in soil physics. Soil physics, as a scientific endeavor, deals with the state and movement of matter and with the fluxes and transformations of energy in the soil and related porous media. (SSSA) Soil Physics 2010 Copyright© Markus Tuller and Dani Or2002-2004
  • 4. Soil Physics 2010 Copyright© Markus Tuller and Dani Or2002-2004
  • 5. Copyright© Markus Tuller and Dani Or2002-2004
  • 6. Soil Structure • Soil structure is the arrangement of particles in the soil • Structure affects aeration, water movement, heat transfer, and root growth • Granular is ideal for agriculture, allows for maximum pore space Copyright© Markus Tuller and Dani Or2002-2004
  • 7. Impact of decline in soil structure on soil physical quality Copyright© Markus Tuller and Dani Or2002-2004
  • 8. Effects of soil structure on ecosystem functions. Copyright© Markus Tuller and Dani Or2002-2004
  • 9. prismatic granular blocky platy single grained columnar massive Copyright© Markus Tuller and Dani Or2002-2004
  • 10. What is Soil Consistency ? •Soil consistence provides a means of describing the degree and kind of cohesion and adhesion between the soil particles as related to the resistance of the soil to deform or rupture. •Since the consistence varies with moisture content, the consistence can be described as dry consistence, moist consistence, and wet consistence. •Consistence evaluation includes rupture resistance and stickiness. The rupture resistance is a field measure of the ability of the soil to withstand an applied stress or pressure as applied using the thumb and forefinger. •Soil consistency is defined as the relative ease with which a soil can be deformed use the terms of soft, firm, or hard. •Consistency largely depends on soil minerals and the water content. Copyright© Markus Tuller and Dani Or2002-2004
  • 11. Copyright© Markus Tuller and Dani Or2002-2004
  • 12. Copyright© Markus Tuller and Dani Or2002-2004
  • 13. Copyright© Markus Tuller and Dani Or2002-2004
  • 14. little or no soil adheres to fingers after release of pressure soil adheres to both fingers after release of pressure with little stretching on separation of fingers soil adheres firmly to both fingers after release of pressure with stretches greatly on separation of fingers Copyright© Markus Tuller and Dani Or2002-2004
  • 15. Soil Consistency - Atterberg Limits Atterberg, a Swedish agriculturist, proposed a concept dividing the entire cohesive range of the soil into five stages and six divisions of soil wetness. These limits, corresponding with soil moisture content from harsh consistency to viscous flow, are called Atterberg constants. Shrinkage Limit, Lower Plastic Limit, Cohesion Limit. Sticky Limit, Upper Plastic Limit , Upper Limit of Viscous Flow. Depending on Moisture Content soil can be divided into: Moisture Content (w) (-) 1. Solid Shrinkage Limit (SL) 2. Semi-Solid LI = 0 3. Plastic 4. Liquid (+) Liquidity Index (LI) Plastic Limit (PL) Plasticity Index (PI) = PL - LL Liquid Limit (LL) LI = 1 Copyright© Markus Tuller and Dani Or2002-2004
  • 16. Copyright© Markus Tuller and Dani Or2002-2004
  • 17. LL: The lowest water content above which soil behaves like liquid, normally below 100. PL: The lowest water content at which soil behaves like a plastic material, normally below 40. PI: The range between LL and PL. Shrinkage limit: the water content below which soils do not decrease their volume anymore as they continue dry out. –needed in producing bricks and ceramics . Lower Plastic limit: This refers to the moisture content corresponding with the lower limit of the plastic range Upper Plastic Limit. This is also called the liquid limit or the lower limit of viscous flow. Copyright© Markus Tuller and Dani Or2002-2004
  • 18. Liquid Limit - Definition Liquid Limit (LL) is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow (Liquid limit of a fine-grained soil gives the moisture content at which the shear strength of the soil is approximately 2.5 kN / m2) Plastic Limit - Defn The moisture content (%) at which the soil when rolled into threads of 3.2mm (1/8 in) in diameter, will crumble. PL = w% at d 3.2 mm (1/8 in.) Copyright© Markus Tuller and Dani Or2002-2004
  • 19. •Casagrande (1932) studied the relationship of the plasticity index to the liquid limit of a wide variety of natural soils. • He proposed a plasticity chart Copyright© Markus Tuller and Dani Or2002-2004
  • 20. Plasticity Index - Definition Plasticity Index is the difference between the liquid limit and plastic limit of a soil. PI = LL – PL Copyright© Markus Tuller and Dani Or2002-2004
  • 21. Shrinkage Limit - Definition The moisture content, in percent, at which the volume of the soil mass ceases to change Copyright© Markus Tuller and Dani Or2002-2004
  • 22. A complex and interactive relationship between Atterberg’s limits, soil tilth, and soil moisture content is shown in Fig. Soil produces a good tilth when cultivated at a moisture content corresponding to a friable consistency or in the vicinity of the lower plastic limit. Soil does not produce clod when plowed at this moisture content. Soils are highly susceptible to compaction and puddling when cultivated within the plastic range. If the lower plastic limit is smaller than field capacity, soil structure may be adversely affected if soil is cultivated at moisture content between the lower plastic limit and the field capacity.  If the lower plastic limit is greater than the field capacity, good soil tilth is produced when it is cultivated at moisture content between the lower plastic limit and field capacity. Copyright© Markus Tuller and Dani Or2002-2004
  • 23. Shrinkage Limit - Measurement Copyright© Markus Tuller and Dani Or2002-2004
  • 24. Copyright© Markus Tuller and Dani Or2002-2004
  • 25. The Atterberg limits are a basic measure of the nature of a fine-grained soil.. Thus, the boundary between each state can be defined based on a change in the soil's behavior. The Atterberg limits can be used to distinguish between silt and clay, and it can distinguish between different types of silts and clays. Why Atterberg Limits ? •Atterberg limits are important to describe the consistency of fine-grained soils •A fine-grained soil usually exists with its particles surrounded by water. •The amount of water in the soil determines its state or consistency •Four states are used to describe the soil consistency; solid, semi-solid, plastic and liquid •The knowledge of the soil consistency is important in defining or classifying a soil type or predicting soil performance when used a construction material. The soil consistency is a practical and an inexpensive way to distinguish between silts and clays Copyright© Markus Tuller and Dani Or2002-2004
  • 26. Copyright© Markus Tuller and Dani Or2002-2004
  • 27. Schematic variation of soil bulk density in non swelling (rigid), moderately swelling and extensively swelling soils. Fig. 2, rigid or non swelling soils do not change their specific volume, ν, and hence, their bulk density ρ during their water content θ variation range. b Rigid or non swelling soils are usually coarse – textured, organic matter – poor, and hard to till. They also have low aggregate stability, high module of rupture, and low resilience after a given damage (e.g. compaction by agricultural traffic). They are considered to have hard-set behavior. Copyright© Markus Tuller and Dani Or2002-2004
  • 28. Schematic variation of soil bulk density in non swelling (rigid), moderately swelling and extensively swelling soils. In contrast, extensively swelling soils undergo significant bulk density, ρb, variations during their water content, θ, variation range. They are usually fine –textured, with smectitic type of clays. They develop desiccation cracks on drying, which confers them high resilience, and little tillage requirement. They are considered to have self-mulch behavior. Copyright© Markus Tuller and Dani Or2002-2004
  • 29. Fig. 3. A hard plow pan developed in the subsoil of a non swelling sandy loam (Haplic Phaeozem) of the Argentine Pampas. After several years of disc plowing, a hard plow pan is developed in the subsoil. Copyright© Markus Tuller and Dani Or2002-2004
  • 30. Fig. 4. Extensively swelling Vertisol of the Argentine Mesopotamia, cropped to soybean using zero tillage Copyright© Markus Tuller and Dani Or2002-2004
  • 31. The process of swelling is mainly caused by the intercalation of water molecules entering to the inter-plane space of smectitic clay minerals ( Parker et al.1982). An schematic visualization of this process is depicted by Fig. 5. Copyright© Markus Tuller and Dani Or2002-2004
  • 32. Consequences of soil swelling Unfavorable effects are  the destruction of buildings, roads and pipelines in uncropped soils, the leaching of fertilizers and chemicals below the root zone through desiccation cracks (by pass flow). In these soils horizontal cracks break capillary flux of water. Favourable effects, swelling clays can be used to seal landfills storing hazardous wastes. This sealing avoids the downward migration of contaminants to ground water . In cropped soils, the development of a dense pattern of cracks on drying improves water drainage and soil aeration, and decreases surface runoff in sloped areas. Soil cracking is closely related to the recovery of porosity damages by compaction. Copyright© Markus Tuller and Dani Or2002-2004
  • 33. Methods for assessing soil swell-shrink potential a) Coefficient of linear extensibility, COLE It characterizes the variation of soil volume from 1/3 atm water retention (i.e. field capacity) to oven dry conditions: where Lm is length of moist sample, Ld is length of dry sample, is wet bulk densit y (measured on plastic coated clods at 0.3 or 0.1 bar suction) and ρb is dry bulk density. A range of soil swell-shrink potential can be distinguished Copyright© Markus Tuller and Dani Or2002-2004
  • 34. SOIL VISCOSITY As soil moisture content increases, its consistency changes from plastic, to sticky, to viscous. When viscous, soil flows under stress and the flow is proportional to the force applied. When plastic, a certain amount of force must be applied before any flow is produced. The flow behavior of a soil is explained by the Bingham equation where V is the volume of flow, μ is the coefficient of mobility, F is the force applied, F′ is the force necessary to overcome the cohesive forces (also called the yield value), or F′ is zero and the volume of flow is proportional to the force. The constant of proportionality k in viscous flow is the coefficient of viscosity of the liquid V=kμ(F−F′) Copyright© Markus Tuller and Dani Or2002-2004
  • 35. SOIL SHRINKAGE Atterberg limits also have an important application to soil shrinkage. Atterberg defined “shrinkage limit” as the soil moisture content below which the soil ceases to shrink, and represents the lower moisture limit of the semisolid state or soft-friable consistency. The process of shrinkage is due to the manifestations of the diffused double layer, and due to the forces of surface tension at the air-water interface. The magnitude of volume change depends of soil structure, Aggregate shape, porosity and pore size distribution, nature, and amount of clay. Therefore, the shrinkage process is related to the change in total volume (Vt) in relation to the change in volume of water (θ) in Normal (upper solid line) and residual (lower solid line) the soil . −3 shrinkage curves for a soil bulk density of 1.1 Mg m . Copyright© Markus Tuller and Dani Or2002-2004
  • 36. Figure which shows two distinct types of shrinkage. The normal shrinkage (curve segment labelled AB) refers to the process in which decrease in total soil volume (Vt) is proportional to the volume of water (θ) withdraw from the soil. The slope of the normal line is an important indicator of the kind of shrinkage. If the angle is 45°, the soil displays a normal shrinkage. If the angle is <45°, the soil displays less than normal shrinkage. The angle of the line of normal shrinkage is an important soil characteristic(Mitchell, 1992) and is influenced by managt. The normal shrinkage continues until the point when there is a strong interaction between particles, and further shrinkage is caused by compression and orientation of particles rather than due to decrease in Vt. This shrinkage is called the residual shrinkage (curve segment labeled BC). Copyright© Markus Tuller and Dani Or2002-2004
  • 37. Application of Shrinkage Soil shrinkage is a rapid process compared with swelling which can continue for several years under confined environments. In agricultural soils, shrinkage is evidenced by formation of cracks.  Soil cracks are large if the soil is cohesive (e.g., Vertisols) and small but numerous when soil is well structured with little cohesion between aggregates.  When soils develop large cracks, there is a considerable damage to plant roots. Roots in a severely cracked soil are confined to the small and dense soil mass between the cracks, thereby decreasing water and nutrient use cracks efficiencies. Roots also affect soil shrinkage (Mitchell and Van Genuchten, 1992). Copyright© Markus Tuller and Dani Or2002-2004
  • 38. SOIL STRENGTH It refers to the capacity of a soil to resist, withstand, or endure an applied stress (σ) without experiencing failure (e.g., rupture, fragmentation, or flow). It is soil’s resistance that must be overcome to cause physical deformation (ε) of a soil mass. It implies the maximal stress which may be induced in soil without causing it to fail. soil strength has applications to root growth, seedling emergence, aggregate stability, erodibility and erosion, compaction and compactability, and draft requirements for plowing Copyright© Markus Tuller and Dani Or2002-2004
  • 39. Factors Affecting Soil Strength Soil Structure. Aggregate size is an important determinant of soil strength. Stress at fracture decreases exponentially with increase in aggregate (clod) diameter. Soil Bulk Density. It determines the magnitude of particle-to-particle contacts. Effects of soil bulk density on soil strength are confounded with those of soil moisture content. Soil strength decreases with increase in total soil volume ln S= − F ln V + A S - soil strength, V - soil volume, A -adjustment factor, and F - soil constant Properties of Soil Solids. Soil constitution (i.e., particle size distribution, clay mineralogy, and soil organic matter concentration) affects soil strength through changes in aggregation, soil bulk density and specific volume, moisture content, and types of pores. Soil Moisture Content. Soil strength increases with decrease in soil moisture content or moisture potential. Soil drying increases strength by increasing capillary cohesion as it increases the effective stress, and compactness by shrinkage For a given bulk density, soil strength decreases with increasing soil moisture content. For 39 a given soil moisture content, soil strength increases with increase in soil bulk density. In general, fine-textured soils at low moisture content exhibit high strength.
  • 40. Strength of different materials Steel Tensile strength Concrete Soil Compressive strength Shear strength Complex behavior Presence of pore water 40
  • 41. Shear Strength of Soils Soil strength may be of two types: (i)resistant to volumetric compression, and (ii)resistant to linear deformation or shear strength. 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. 41 Copyright© Markus Tuller and Dani Or2002-2004
  • 42. SHEAR STRENGTH OF SOILS: Necessity of studying Shear Strength of soils : • Soil failure usually occurs in the form of “shearing” along internal surface within the soil. • Thus, structural strength is primarily a function of shear strength. Shear Strength: • The strength of a material is the greatest stress it can sustain. • The safety of any geotechnical structure is dependent on the strength of the soil. • If the soil fails, the structure founded on it can collapse. Copyright© Markus Tuller and Dani Or2002-2004
  • 43. 44
  • 44. Mass Wasting: Shear Failure 45
  • 45. Shear Strength in Soils :  The shear strength of a soil is its resistance to shearing stresses.  It is a measure of the soil resistance to deformation by continuous displacement of its individual soil particles.  Shear strength in soils depends primarily on interactions between particles.  Shear failure occurs when the stresses between the particles are such that they slide or roll past each other 46
  • 46. Components of shear strength of soils Soil derives its shear strength from two sources: – Cohesion between particles (stress independent component) • Cementation between sand grains • Electrostatic attraction between clay particles – Frictional resistance and interlocking between particles (stress dependent component) Cohesion (C), is a measure of the forces that cement particles of soils 47
  • 47. Internal Friction : Internal Friction angle (f), is the measure of the shear strength of soils due to friction 48
  • 48. Stresses: Gravity generates stresses (force per unit area) in the ground at different points. Stress on a plane at a given point is viewed in terms of two components: Normal stress (σ) : acts normal to the plane and tends to compress soil grains towards each other (volume change) Shear stress (t ): acts tangential to the plane and tends to slide grains relative to each other (distortion and ultimately sliding failure) 49
  • 49. Stress refers to the force per unit area. For a given plane at a point, the resultant stress vector may be divided into two components: normal and tangential stress. Normal Stress (σ). Normal stress is caused by a force vector perpendicular to the area of action σ =Fn/A where Fn is the force acting normal to the area A. The transmitted normal stress generally decreases with distance from the applied load and with distance from its line of action. Tangential Stress (τ) or Shearing Stress. This stress is caused by a force vector parallel to the area of action τ =Ft/A where Ft is the tangential force acting on area A. 50
  • 50. Definition of stress and strain The reaction of a solid body to a force F or a combination of forces acting upon or within it can be characterized in terms of its relative deformation or strain. The ratio of force to area where it acts is called stress. normal stress σ = Fn / A shear stress τ = Fs / A normal strain ε = δz / zo shear strain γ = δh / zo Note that compressive stresses and strains are positive and counter-clockwise shear stresses and strains are positive. Copyright© Markus Tuller and Dani Or2002-2004
  • 51. Shear strength of soil is “The capacity of a soil to resist the internal and external forces which slide past each other” 52
  • 52. Factors Influencing Shear Strength: The shearing strength, is affected by: – Soil composition: mineralogy, grain size and grain size distribution, shape of particles, pore fluid type and content, ions on grain and in pore fluid. – Initial state: State can be describe by terms such as: loose, dense, over consolidated, normally consolidated, stiff, soft, etc. – Structure: Refers to the arrangement of particles within the soil mass; the manner in which the particles are packed or distributed. Features such as layers, voids, pockets, cementation, etc, are part of the structure. Copyright© Markus Tuller and Dani Or2002-2004
  • 53. Total vs. effective stresses When a load is applied to soil, it is carried by the water in the pores as well as the solid grains. The increase in pressure within the pore water causes drainage (flow out of the soil), and the load is transferred to the solid grains. The rate of drainage depends on the permeability of the soil. The strength and compressibility of the soil depend on the stresses within the solid granular fabric. These are called effective stresses. Copyright© Markus Tuller and Dani Or2002-2004
  • 54. Formulation of Shear Strength of Soil: • In reality, a complete shear strength formulation would account for all previously stated factors. • Soil behavior is quite complex due to the possible variables stated. Coulomb Failure Criterion : Coulomb stated that “the shear stress at failure is a function of normal stress” and is given by: Charles Augustin de Coulomb (1736 - 1806) Copyright© Markus Tuller and Dani Or2002-2004
  • 55. Charles Mohr The Mohr Failure Criterion: Mohr presented in 1900 a theory of rupture of materials, that was the result of a combination of both normal and shear stresses. The shear stress at failure is thus a function of normal stress and the Mohr circle is tangential to the functional relationship given by Coulomb Copyright© Markus Tuller and Dani Or2002-2004
  • 56. The Mohr-Coulomb Failure Criterion: This theory states that: “a material fails because of a critical combination of normal stress and shear stress, and not from their either maximum normal or shear stress alone” Copyright© Markus Tuller and Dani Or2002-2004
  • 57. Copyright© Markus Tuller and Dani Or2002-2004
  • 58. Copyright© Markus Tuller and Dani Or2002-2004
  • 59. Copyright© Markus Tuller and Dani Or2002-2004
  • 60. Soil strength – undrained shear The maximum value of stress that may be sustained by a material is termed strength. The strength is independent of the normal stress  since the response to loading simple increases the pore water pressure and not the effective stress. The shear strength τ f is a material parameter which is known as the undrained shear strength su. τ f = (σ a - σ r) = constant Copyright© Markus Tuller and Dani Or2002-2004
  • 61. Soil strength – the angle of friction The strength increases linearly with increasing normal stress and is zero when the normal stress is zero. τ'f = σ'n tanφ‘ where, φ' is the angle of friction In the Mohr-Coulomb criterion the material parameter is the angle of friction f’ and materials which meet this criterion are known as frictional.  In soils, the Mohr-Coulomb criterion applies when the normal stress is an effective normal stress. Copyright© Markus Tuller and Dani Or2002-2004
  • 62. Soil strength - cohesion •.. The strength increases linearly with increasing normal stress and is positive when the normal stress is zero. τ'f = c' + σ'n tanφ' φ' is the angle of friction c' is the 'cohesion' intercept In soils, the Mohr-Coulomb criterion applies when the normal stress is an effective normal stress. Copyright© Markus Tuller and Dani Or2002-2004
  • 63. Typical values of φ‘, c’ and su Undrained shear strength Hard soil Stiff soil Firm soil Soft soil Very soft soil Drained shear strength Sands Clays Precompression stress Pv soft firm stiff su > 150 kPa su = 75 ~ 150 kPa su = 40 ~ 75 kPa su = 20 ~ 40kPa su < 20 kPa c´ (kPa) 0 0 - 30 kPa φ´ (deg) 30° - 45° 0 - 20° 0-50 kPa 50-150 kPa > 150 kPa Copyright© Markus Tuller and Dani Or2002-2004
  • 64. Mohr Theory of Soil Strength This theory is based on the functional relationship between normal stress (σ) and tangential or shearing stress (τ). The envelope of the family of circles is used as a criterion of shearing strength of soil. When a series of stress states just sufficient to cause failure is imposed on the same soil material, these states can be plotted as a set or family of Mohr circles. The line tangent of these circles, called the envelope of the family of circles, is used as a criterion of shear strength. When this envelope is a straight line, it can be described mathematically by Eq. τ = τo + bσ The intercept (τ o) is the shear stress needed to cause failure when normal stress (σ) is zero, and is called soil cohesion (C) or cohesiveness. Substituting these terms in Eq. yields following Eq. used to express soil shear strength. 65
  • 65. The functional relationship between shearing stress (τ) and normal stress (σ) is given by Mohr’s circle (a or τo is the intercept and constant b is the tangent of angle Φ Copyright© Markus Tuller and Dani Or2002-2004
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  • 67. TRIAXIAL COMPRESSION TEST Failure Surface By Kamal Tawfiq, Ph.D., P.E.
  • 68. Triaxial Compression Test 1- Applying Confining Stresses 2- Loading )F F2 Each Circle = One Test F2 F2 F2 F2 3- At Failure Deviator stress = ) Ff + F2 Axial = F1 stress Confining stress = F2 F2 F2 J F2 2 F2 F2 + F1 = Major Principle Stress F2 = Minor Prencipal Stress + Failure Surface + )F ) Ff )F = deviator stress = F1 Failure Surface Cohesion = c F2 2 F2 F2 F 1 F1 F1 Fn By Kamal Tawfiq, Ph.D., P.E.
  • 69. Copyright© Markus Tuller and Dani Or2002-2004
  • 70. Soil Compaction Dr. P.K. Mani Department of Agril. Chemistry and Soil Science Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India E-mail:, Website: Copyright© Markus Tuller and Dani Or2002-2004
  • 71. Soil Compaction – desired or not? • In agriculture and forestry soil compaction is undesirable. • For many engineering applications a well compacted soil is crucial for safe foundations (the Leaning Tower of Pisa is an example of building on soft soil). Image: Opera Primaziale Pisana Copyright© Markus Tuller and Dani Or2002-2004
  • 72. Soil Compaction in the Field: 5- Sheep foot Roller 1- Rammers 2- Vibratory Plates 6- Dynamic Compaction 3- Smooth Rollers 4- Rubber-Tire Copyright© Markus Tuller and Dani Or2002-2004
  • 73. Porosity value generally ranges from 0.3 to 0.6 (30–60%). In clayey soils, the porosity is highly variable because the soil alternately swells, shrinks, aggregates, disperses, compacts, and cracks it ranges between 0.3 and 2. Copyright© Markus Tuller and Dani Or2002-2004
  • 74. Definition: Soil compaction is defined as the method of mechanically increasing the density of soil by reducing volume of air. γsoil (2) > γsoil (1) Load Air Air Water Water Soil Matrix Compressed soil Solids Solids γsoil (1) = WT1 VT1 γsoil (2) = WT1 VT2 Copyright© Markus Tuller and Dani Or2002-2004
  • 75. Copyright© Markus Tuller and Dani Or2002-2004
  • 76. Why Soil Compaction: 1- Increase Soil Strength 2- Reduce Soil Settlement 3- Reduce Soil Permeability 4- Reduce Frost Damage 5- Reduce Erosion Damage Water is added to lubricate the contact Factor Affecting Soil Compaction: surfaces of soil 1- Soil Type particles and improve 2- Water Content (w c) the compressibility of 3- Compaction Effort Required (Energy) Types of Compaction : (Static or Dynamic) the soil matrix 1- Vibration 2- Impact 3- Kneading 4- Pressure Water is added to lubricate the contact surfaces of soil particles and improve the compressibility of the soil matrix Copyright© Markus Tuller and Dani Or2002-2004
  • 77. Soil Compaction in the Lab: 1- Standard Proctor Test 2- Modified Proctor Test 3- Gyratory Compaction Standard Proctor Test Modified Proctor Test Gyratory Compaction Copyright© Markus Tuller and Dani Or2002-2004
  • 78. Copyright© Markus Tuller and Dani Or2002-2004
  • 79. Copyright© Markus Tuller and Dani Or2002-2004
  • 80. Copyright© Markus Tuller and Dani Or2002-2004
  • 81. Copyright© Markus Tuller and Dani Or2002-2004
  • 82. Effect of Soil Type: The soil type - that is, grain-size distribution, shape of the soil grains, speciific gravity of soil solids, and amount and type of clay minerals presenthas a great influence on the maximum dry unit weight and optimum moisture content Copyright© Markus Tuller and Dani Or2002-2004
  • 83. 4 types of compacn curves encountered in soils Type A compaction curves are those that have a single peak. This type of curve is generally found for soils that have a liquid limit between 30 and 70. Curve type B is a one-and-onehalf-peak curve, and curve type C is a doublepeak curve. Compaction curves of types B and C can be found for soils that have a liquid limit less than about 30. Compaction curves of type D do not have a definite peak. They are termed odd shaped. Soils with a liquid limit greater than about 70 may exhibit compaction curves of type C or D. Such soils are uncommon. Copyright© Markus Tuller and Dani Or2002-2004
  • 84. Agricultural Soil Compaction – Causes Operation of heavy vehicles (e.g. harvesters, construction machines) on agricultural land can cause soil compaction. Copyright© Markus Tuller and Dani Or2002-2004
  • 85. SOIL COMPACTION Soil compaction can be conceptually viewed in a dynamic or a static situation, and in practical applications. • Dynamic situation, it is a physical deformation or a volumetric strain. • Static situation, it is the characteristic related to soil resistance to increase its bulk density. • In practice, soil compaction is a process leading to compression of a mass of soil into a smaller volume and deformation resulting in decrease in total porosity and macroporosity and reduction in water transmission and gaseous exchange. • The degree or severity of soil compaction is expressed in terms of soil bulk density (ρb), total porosity(ft), aeration porosity (fa), and void ratio (e). The volume decrease is primarily at the cost of soil air, which may be expelled or compressed. The compression of soil solids (i.e.,change in ρs) and water (i.e., change in ρw) is evidently not possible. Copyright© Markus Tuller and Dani Or2002-2004
  • 86. Compression of a moist soil due to external load may displace the liquid and increase the contact area between two particles (Fig.). The magnitude of increase in contact area depends on the degree of rearrangement or deformation of the particles. The menisci formed by the liquid may also change due to differences in the contact area. The shape of the meniscus depends on surface tension forces, which are usually small compared with the external load. The deformation may be elastic and soil particles may regain their original shape when the applied load is released. Copyright© Markus Tuller and Dani Or2002-2004
  • 87. The degree of deformation and rearrangement depends on soil structure and aggregation, and on the extent to which soil particles can change position by rolling or sliding. For partly saturated clayey soils, the volume change depends on reorientation of the particles and displacement of water between particles. The particle rearrangement may lead to closed packing with attendant decrease in void ratio.  e=eo−c log P/Po where eo = void ratio at the initial pressure Po, c = slope of the curve on semilogrithmic plot, and P = applied pressure that changed the final void ratio to e. Degree of soil compaction may also be expressed in terms of total porosity in relation to the external load (Soehne, 1958) . ft = −A lnP+f10 where ft is total porosity, f10 is the porosity obtained by compacting loose soil at a pressure of 10 PSI, A is the slope of the curve, and P is the applied pressure. Copyright© Markus Tuller and Dani Or2002-2004
  • 88. Soil compaction is extremely relevant to • Agriculture because of its usually adverse impact on root development and crop yields; • Civil engineering because of its relation to settlement, stability, and groundwater flow; and to • Environments because of its effects on erosion, anaerobiosis, transport of pollutants in surface and sub-surface flow, and nature and rate of gaseous flow from soil to the atmosphere. From an agricultural perspective especially in relation to plant root growth, there is an optimal range of soil bulk density, which for most soils is <1.4 Mg/m3. However, the optimum range of soil bulk density may differ among soils and crops (Kyombo and Lal, 1994). For some soils (e.g., Andisols or soils of volcanic origin) the optimal density may be as low as 1.0. A similar case may be in soils containing a high level of soil organic matter content. It is precisely because of these differences in response to bulk density that effects of compaction on crop yield are highly soil-dependent Copyright© Markus Tuller and Dani Or2002-2004
  • 89. Soil Compactibility Soil compaction or densification happens due to external load or force applied to the soil. The force applied per unit area is defined as stress, which may be normal stress when it is perpendicular to the soil ; shear stress when it has a tangential component. Compression is the process of increase in soil mass per unit volume due to external load. The load may be static or dynamic. The latter is applied in the form of vibration, rolling, or trampling. While compression in unsaturated soils is called “compaction,” that in saturated soils is termed “consolidation.” Soil compressibility is the “resistance of a soil against volume decrease by external load.” In comparison, soil compactability is the difference between the initial bulk density and the maximum bulk density to which a soil can be compacted by a given amount of energy at a defined moisture content. Copyright© Markus Tuller and Dani Or2002-2004
  • 90. WHAT ARE THE CONSEQUENCES OF SOIL COMPACTION FOR PLANT GROWTH? Soil compaction can have both desirable and undesirable effects on plant growth. Desirable Effects •Slightly compacted soil can speed up the rate of seed germination because it promotes good contact between the seed and soil. In addition, moderate compaction may reduce water loss from the soil due to evaporation and, therefore, prevent the soil around the growing seed from drying out. Corn planters have been designed specifically to provide moderate compaction with planter mounted packer wheels that follow seed placement. •A medium-textured soil, having a bulk density of 1.2 g/cc , is generally favorable for root growth. • However, roots growing through a medium-textured soil with a bulk density near 1.2 g/cc will probably not have a high degree of branching or secondary root formation. •In this case, a moderate amount of compaction can increase root branching and secondary root formation, allowing roots to more thoroughly explore the soil for nutrients. This is especially important for plant uptake of non-mobile nutrients such as phosphorus. Copyright© Markus Tuller and Dani Or2002-2004
  • 91. Undesirable Effects • Excessive soil compaction impedes root growth and therefore limits the amount of soil explored by roots. This, in turn, can decrease the plant's ability to take up nutrients and water. •From the standpoint of crop production, the adverse effect of soil compaction on water flow and storage may be more serious than the direct effect of soil compaction on root growth. •In dry years, soil compaction can lead to stunted, drought stressed plants due to decreased root growth. Fig.2. Nitrogen deficiency symptoms in corn. •Soil compaction in wet years decreases soil aeration. This results in increased denitrification . • There can also be a soil compaction induced nitrogen and potassium deficiency (see Fig. 2 & 3). Plants need to spend energy to take up potassium. • Reduced soil aeration affects root metabolism. All of these factors result in added stress to the crop and, ultimately, yield loss. Fig. 3. Potassium deficiency symptoms in corn. Copyright© Markus Tuller and Dani Or2002-2004
  • 92. Research from North America and Europe indicates that crops respond to soil compaction as shown in Figure 4. • In a dry year, at very low bulk densities, yields gradually increase with an increase in soil compaction. Soon, yields reach a maximum level at which soil compaction is also optimal for the specific soil, crop, and climatic conditions. However, as soil compaction continues to increase beyond optimum, yields begin to decline. •With wet weather, yields are decreased with any increase in compaction. Fig. 4. Effects of weather on crop yield response to compaction level (Soane et al., 1994). Copyright© Markus Tuller and Dani Or2002-2004
  • 93. Due to the increase in bulk density, the porosity of soil decreases. Large pores (called macropores), essential for water and air movement in soil, are primarily affected by soil compaction. Research has suggested that most plant roots need more than 10 percent airfilled porosity to thrive. Total porosity and macroporosity were greatly reduced in an original and a subsoiled but subsequently recompacted plow pan compared to an uncompacted pasture. ( Kooistra, and Boersma. 1994. Soil Tillage Research 29:237–247.) Copyright© Markus Tuller and Dani Or2002-2004
  • 94. The surface of long-term, no-till soil cannot be compacted to as great a density as conventionally tilled soil due to higher organic matter contents. (Thomas, et al.,1996) No-till has a lot of advantages over tillage—reduced labor requirements, reduced equipment costs, less runoff and erosion, increased drought resistance of crops, and higher O.M. content and biological activity. •The higher O.M. content and biological activity in no-till makes the soil more resilient to soil compaction. Topsoil from long-term no-till and conventional till fields were subject to a standard compaction treatment at different moisture contents. The “Proctor Density Test” is used to determine what the maximum compactability of soil is. The conventional till soil could be compacted to a maximum density of 1.65 g/cm3, which is considered root limiting for this soil. The no-till soil could only be compacted to 1.40 g/cm3, which is not considered root limiting. Thus, topsoil compaction would be less of a concern in no-till fields. Copyright© Markus Tuller and Dani Or2002-2004
  • 95. this vicious compaction/ tillage spiral is an environmental threat with impacts beyond the individual field.(Duiker, 2004) More tillage operations and more power are needed to prepare a seedbed in compacted soil. This leads to increased pulverization of the soil and a general deterioration of soil structure, which makes the soil more sensitive to recompaction. Therefore, compaction can enforce a vicious tillage spiral that degrades soil and results in increased emissions of the greenhouse gases CO2, CH4, NO2 due to increased fuel consumption and slower water percolation. Ammonia losses also increase because of decreased infiltration in compacted soil. More runoff will cause increased erosion and nutrient losses to surface waters. At the same time, reduced percolation through the soil profile restricts the potential for gw (ground water) recharge from compacted soils. Copyright© Markus Tuller and Dani Or2002-2004
  • 96. The most direct effect of soil compaction is an increase in the bulk density of soil. Optimum bulk densities for soils depend on the soil texture . Whenever the b.d . exceeds a certain level, root growth is restricted.. A note of caution must be made here in respect to the effects of tillage on bulk density . No-till soils often have a higher bulk density than recently tilled soils. However, because of higher organic matter content in the topsoil and greater biological activity, the structure of a no-till soil may be more favorable for root growth than that of a cultivated soil, despite the higher bulk density. Copyright© Markus Tuller and Dani Or2002-2004
  • 97. •Soil compaction causes a decrease in large pores (called macropores), resulting in a much lower water infiltration rate into soil, as well as a decrease in saturated hydraulic conductivity. •Unsaturated hydraulic conductivity sometimes increases due to compaction. Unsaturated hydraulic conductivity is important when water has to move to roots. Thus, compacted soils are sometimes not as drought sensitive as uncompacted soils— assuming the root system is of equal size in both cases, which is usually not the case. Typically, the net effect of compaction is that crops become more easily damaged by drought because of a small root system. Copyright© Markus Tuller and Dani Or2002-2004
  • 98. Management of Soil Compaction in Agricultural Lands There are two strategies of soil compaction management: (i) minimizing risks of soil compaction or compaction prevention, and (ii) compaction alleviation . Preventive strategies are economic and have less adverse impacts on crop yields and environments than the curative measures of compaction alleviation (Larson et al., 1994). •A useful strategy to prevent soil compaction is to minimize the vehicular traffic to the absolutely essential by reducing the number and frequency of operations, and performing farm operations only when the soil moisture content is below the optimal range for the maximum proctor density. • Mulch farming and conservation tillage (Lal, 1989; Carter, 1994) reduce the risk of soil compaction for some soils and environments. • Guided traffic system, low ground pressure tires (Vermeulen and Perdok, 1994), adoption of dual tires, and wide tires are other innovative ideas of decreasing pressure on soil. • The guided traffic system involves confining vehicular traffic to permanent narrow lanes and reducing the fractional area affected by traffic wheels to as little as possible (Taylor,1994). Copyright© Markus Tuller and Dani Or2002-2004
  • 99. MANAGING SOIL COMPACTION Avoid trafficking wet soil. Only wet soil can be compacted. Fields should not be trafficked if they are at or wetter than the plastic limit  Keep axle loads below 10 tons. Subsoil compaction is caused by axle load and is basically permanent. Decrease contact pressure by using flotation tires, doubles, or tracks. Topsoil compaction is caused by high contact pressure. To reduce contact pressure, a load needs to be spread out over a larger area. This can be done by reducing inflation pressure. A rule of thumb is that tire pressure is the same as contact pressure. Tires inflated to 100 psi such as truck road tires should be kept out of the field Decrease trafficked area by increasing swath and vehicle width or by decreasing number of trips. Reduce the area of a field that is subject to traffic by increasing swath width of manure spreaders or the spacing between wheels so individual wheel tracks are more widely spaced. Increase soil organic matter content and soil life. Soil that has high organic matter content and thrives with soil organisms is more resistant to compaction and can better recuperate from slight compaction damage. Copyright© Markus Tuller and Dani Or2002-2004
  • 100. Use tillage sparingly •Soil tillage should be used sparingly to alleviate compaction when no other means can be used. •Growers should avoid falling into the vicious compaction/tillage spiral as explained earlier. •If any tillage is done, try to leave as much crop residue as possible at the soil surface to protect against erosion and to use as a food source for certain soil organisms such as earthworms. •Noninversion tillage is preferable. •If possible, perform tillage only in the seed zone. Copyright© Markus Tuller and Dani Or2002-2004
  • 101. The vehicle load can be distributed over a large area by using dual tires or wide tires. The soil compaction hazard is less when the load is distributed over a large area. Subsoiling by chisel plow can decrease bulk density and reduce soil strength temporarily. The long-term goal is to create stable biochannels in the subsoil. Crop residue mulch in a no-till farming system buffers the impact of heavy vehicles and minimizes the risk of soil compaction Copyright© Markus Tuller and Dani Or2002-2004
  • 102. Soil Crusting Dr. P. K. Mani Department of Agril. Chemistry and Soil Science Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India E-mail:, Website: Copyright© Markus Tuller and Dani Or2002-2004
  • 103. Soil crust or surface seal, refers to the thin dense layer on the soil surface characterized by low porosity, high density, and low permeability to air and water. Crusting is a soil surface phenomena caused by susceptibility of aggregates at the soil-air interface to disruptive forces of climatic elements and perturbations caused by agricultural practices (e.g., tillage and traffic). Slaking, deflocculation, or dispersion of aggregates on rapid wetting or submersion in water, is attributed to  numerous factors including the effect of entrapped air, predominance of Na+ on the exchange complex, and weak aggregate strength caused by low level of soil organic matter content and weak ionic bonds. (Sumner and Stewart ,1992). Dispersion, reorientation of dispersed particles, drying, and desiccation, lead to formation of a thin crust on the soil surface. Copyright© Markus Tuller and Dani Or2002-2004
  • 104. Crusted condition with high surface roughness due to raindrop Copyright© Markus Tuller and Dani Or2002-2004
  • 105. •A physical crust is a thin layer with reduced porosity and increased density at the sur face of the soil. • A biological crust is a living community of lichen, cyanobacter ia, algae, and moss growing on the soil sur face and binding it together . • A chemical crust or precipitate is white or pale colored and forms in soils with a high content of salts. Both chemical and biological crusts can form on and extend into a physical crust. Properties of Crust The crusted layer is more dense but may be of similar textural makeup than the unaffected soil beneath it. The crust is primarily characterized by reduction in total volume, size, shape, and continuity of pores. Thickness of the crust may range from <1mm to 10 mm (Norton, 1987). Very thin crusts are called “skin seal.” These microlayers are usually <0.1 mm thick, extremely dense with no visible pores (McIntyre, 1958).  Skin seals may be formed by reorientation of fine dispersed particles and/or washedin-fine material that plug the larger pores. The magnitude of reduction in porosity of the crust may range from 30 to 90%, with corresponding decrease in pore size. The pore diameter in the crust may be as small as 0.075 mm (Valentin and Figueroa, 1987). Copyright© Markus Tuller and Dani Or2002-2004
  • 106. Soil structure at extreme scales. Left: textural porosity in the clay mineral kaolinite. The scale bar is 0.004 mm. Many of the pores visible are small enough to retain water that is not available to plants. Right: structural porosity in a “selfmulching” clay soil with well-defined aggregates and large pores that play a role in drainage, aeration, root growth and the activities of soil fauna. Copyright© Markus Tuller and Dani Or2002-2004
  • 107. Soil Crusts : General Aspects A. Types The two main types of soil crusts generally recognized are structural and depositional crusts (Shainberg, 1985). •The structural crusts are formed due to the shattering effect of raindrops on an otherwise structurally more stable soil surface, followed by a reorientation of soil particles, • depositional crust is formed by sedimentation of particles from standing or slowly flowing water. several other types have been recognized and described, for example, (i)White saline crusts resulting from salt accumulation near the soil surface (e.g. Brabant and Gavaud, 1985); (ii) Black saline crusts due to an accumulation of sodium carbonate (Aubert, 1976); and (iii) Yellow saline crusts on very acid sulphate soils (Le Brusq et al., 1987) composed mainly of aluminium, iron and magnesium sulphates. Copyright© Markus Tuller and Dani Or2002-2004
  • 108. Diagram showing processes involved and sequence of formation of the various types of crusts (after Bresson and Valentin, 1990). Copyright© Markus Tuller and Dani Or2002-2004
  • 109. Mode of formation Casenave and Valentin (1989) distinguished four main processes : (i) wetting, (ii) raindrop impact, (iii) runoff and (iv) drying. Wetting is important in loamy and clayey soils. When dry soil is rapidly wetted, air entrapment occurs and pressure differences disrupt soil aggregates. Swelling occurring concurrently, further aids the disruption process (Valentin,1991). Oversaturation of the uppermost few millimeters of soil results in suspended, dispersed clay which fills the particle interstices, thus forming a structural type surface crust. Slaking of dry aggregates due to rapid wetting can occur independently of impact forces. Raindrop impact is the main cause of crusting on sandy soils. Sandy aggregates are quite fragile and therefore readily break down under raindrop impact. Crater-like features develop at the surface, with coarser particles on top of finer ones. This sorting process, together with the accumulation of finer particles above the zone compacted by raindrops or above the zone of a compressed air layer (Collinet, 1988), are considered to be the most significant processes in the formation of Structural 1 and Structural 2 types of surface crusts . Copyright© Markus Tuller and Dani Or2002-2004
  • 110. During a light rainfall (intensity 0.1 mm h-1) drops of median diameter 1.25 mm, velocity 4.8 ms-1 falling at a rate of 280 m-2 s-1 were recorded (Lull, 1959, Morin, 1993). The associated kinetic energy measured per unit area and time was 12 J m-2 h-1. (Kinetic energy, E= ½ mv2, where m is the mass of rain per unit area and v is the impact velocity of rain drop)  Heavy rainfall of intensity 15 mm h-1 was associated with larger drops, 2.05 mm median diameter, greater fall velocity 6.7 m s-1, fell at a rate of 495 drops m-2 s-1 with a kinetic energy of 340 J m-2 h-1.  During a cloudburst intensities of 1100 mm h-1 may occur which, depending on the drop diameter can give rise to a kinetic energy of 3300 J m-2 h-1 or greater. Copyright© Markus Tuller and Dani Or2002-2004
  • 111. Runoff results in lateral movement of particles, combined with sorting. It favors the formation of a dense, laminated crust referred to as a "runoff depositional" crust. When surface roughness decreases, runoff velocity (or wind velocity) increases. The one or two sandy microlayers of the Structural 2 or Structural 3 crust types are washed away, exposing the denser seal composed of fine particles, or the Structural 1 crust may be smoothed. If the process proceeds leaving coarser gravel behind, a gravel crust develops. Drying increases the strength of a surface crust exponentially as a function of decreasing water content (Valentin, 1986). Cracks and a curling up of platy structures can occur due to differences in shrinkage forces among the microlayers. This phenomenon is pronounced in the case of sedimentary crusts. Copyright© Markus Tuller and Dani Or2002-2004
  • 112. III. Methods Employed in the Study of Soil Crusts A. Microscopy1. Micromorphological studies The microscopic study of thin sections provides a powerful method for examining soil surface crusts. It helps in characterizing the size and nature of the components and the arrangement and porosity of the microlayers forming the crusts. Micromorphology was used to study surface crusts of saline soils in Egypt 2. Electronmicroscopy Back-scattered electron scanning imagery (BESI) of thin sections is more satisfactory, making clear delineation of the microlayers possible (Bresson and Valentin, 1990). A further advantage of this technique is that information on porosity is gained for a region just a few micrometers below the crust surface. Copyright© Markus Tuller and Dani Or2002-2004
  • 113. Crust Strength Measurements Crust strength was measured using the modulus of rupture technique (Richards, 1953). It was found that the modulus of rupture is strongly dependent on the bulk density of the bricquettes, irrespective of the method used to increase bulk density. S = 3FL/2bd2 Where S is the modulus of rupture in dyne/cm2, F is the breaking force in dyne [the breaking force in grams weight (the mass of water needed for breaking the briquettes placed on two supports on a one-handle scale) × 980), L is the distance between the two lower supports, (cm) b is the width of the briquettes, (cm) and d is the depth or thickness of the briquettes (cm). The bar is a CGS unit of pressure and equal to one million 2 2 Copyright© Markus Tuller and Dani Or2002-2004
  • 114. The methodology used for measuring modulus of rupture (MR) as an index of crusting was that proposed by Reeve (1965). Soil particles were collected after passing through 2.00 mm sieve and poured in an aluminum rectangle mold (7 cm×3.5 cm×1 cm) which was alighted on a screen covered with a filter paper. The internal surface of mold was carefully covered with a thin layer of petroleum jelly to prevent the soil particles from adhering to the mold. The excess soil was striked off by a leveler. By adding distilled water from the beneath of the screen, soils soaked well for 30 min. Then the samples were dried at 50oC in oven. The briquettes were carefully removed to measure the pressure needed for breaking them using the equation: 2 S = 3FL/2bd Copyright© Markus Tuller and Dani Or2002-2004
  • 115. Factors Affecting Crust Formation Some soils are undoubtedly more prone to crusting than others. The permanence of a crust formed under conditions of water application also varies greatly - e.g. self-mulching clay soils have a discontinuous crust, but when wet and other conditions favoring crusting prevail, a very dense crust with low hydraulic conductivity may form. The factors involved in soil crusting may be grouped into two classes : (A) those intrinsic to the soil and those due to (B)external influences A. Intrinsic Soil Properties 1. Soil texture Soil particle size distribution, particularly clay and gravel/cobble contents and relative proportions of the various soil separates, affect soil crusting. High clay contents generally favor aggregation and reduce the rate of crust formation, although clay mineralogy and exchangeable cation composition will modify this generalization. Medium-textured soils (< 20% clay) are usually very susceptible to crusting. It is probable that in extremely sandy soils the amount of clay, once dispersed, is not sufficient to clog the conducting pores at the soil surface. Copyright© Markus Tuller and Dani Or2002-2004
  • 116. Several studies have shown that the texture most prone to crusting consists of approximately 90% sand and 10% silt or clay Surface gravel and cobbles may either increase or decrease soil crusting. In the arid zone of west Africa, soils containing coarse fragments are usually severely crusted (Casenave and Valentin, 1989). Conversely, in wet savannah and in the rainforest zone, gravel originating from disintegrated Iron pans usually remains free on an uncrusted topsoil . (Collinet and Valentin,1979). In other studies, coarse fragments protected the smaller surface aggregates from raindrop impact - in the same way as a mulch – thus increasing infiltration and reducing erosion(Collinet and Valentin, 1984) Copyright© Markus Tuller and Dani Or2002-2004
  • 117. 2. -Clay mineralogy Miller(1987), concluded that if the dominant clay mineral of the clay fraction is kaolinite, crusting should be less serious, although the presence of even small amounts of smectite and/or micaceous minerals could drastically increase the soil's crusting tendency. Furthermore, the presence of free iron in soils from the humid to subkumid tropics would also have a stabilizing effect. 3. Carbon content organic matter is one of the most important aggregate stabilizing agents in soil. The positive effect of organic matter on structural stability is more pronounced on sandy than on the more finer textured soils. If the ratio R = organic matter (%)/(silt + clay)(%) is considered, then 4 classes of soil with regard' to crusting hazard were distinguished. Crusting hazard is greatest when R <5% and least when R > 9%. The threshold between low and high crusting susceptibility occurred when R =7%. R <5 : severe physical degradation 5<R<7 : high hazards of physical degradation 7 < R< 9 : low hazards of physical degradation, 9 < R : no physical degradation Copyright© Markus Tuller and Dani Or2002-2004
  • 118. Organic carbon percentage in the soil very clearly determined the MWD of water-stable aggregates. The MWD increased from about 0.3 mm at 1.1 % organic carbon to 3 mm when the organic carbon increased to about 2.4 % 4. Sesquioxide content The stabilising effect of Fe and Al hydrous oxides and oxides are commonly regarded as an important factor in aggregate formation. Farres (1987) tested the aggregate stability of 20 soils from Mozambique and found that higher amounts of iron were associated with greater soil stability to the effects of raindrop impact. The positive effect of a high Fe203 + Al2O3 content on maintaining a good infiltration rate under simulated rain was shown by Smith (1990). With increasing degree of weathering (climatic factors), the silica: sesquioxide ratio increased and resistance to crusting decreased Copyright© Markus Tuller and Dani Or2002-2004
  • 119. 5. Exchangeable cations It is well known that a high percentage of exchangeable sodium (high ESP) and in some cases of exchangeable Mg, favors clay dispersion ( van der Merwe and Burger, 1969). This in turn would increase soil crusting. In this regard the critical ESP (or critical EMgP), that is, the ESP below which crusting is not affected by ESP, is of the utmost importance, particularly in the case of irrigated soils. Levy and van der Watt (1988) studied the effects of clay mineralogy and soil sodicity on crusting of four South African soils. The effect of ESP on crusting differed widely : some soils were hardly affected, others affected at high ESP only and others were affected at all ESP levels. In all cases, a crust did form on the soil surface; the ease and rate of crust formation are apparent from the infiltration rate versus cumulative infiltration curves. Copyright© Markus Tuller and Dani Or2002-2004
  • 120. 6. Topography and microtopography Crusting processes, especially those related to kinetic energy of rain, are most pronounced on very low gradients. On steeper slopes, runoff and surface layer removal can be sufficient to remove the crust as it forms, thus preventing the sharp decrease in infiltration rate usually observed. Microtopography and surface roughness affect crust formation and runoff in that the depth of water films at the soil surface, microslopes and water flow velocity are all influenced on a meso-scale. The result is that a number of crust types and the severity of crusting varies from the depressions to the tops of "mounds" (Levy et al., 1988). Thus runoff depositional or sedimentary crusts develop in the depressions whereas structural and erosional crusts are located on the more elevated zones. Copyright© Markus Tuller and Dani Or2002-2004
  • 121. B. External Factors 1. Kinetic energy of rain Since the energy with which a falling water drop strikes the soil surface is clearly related to its shattering effect on the aggregates, measurement or calculation of the kinetic energy of water drops striking the soil surface is very relevant. Both drop size (mass) and impact velocity, determine kinetic energy, and the latter depends on the former. Valentin and Ruiz Figueroa (1987), using rains with different kinetic energies and various types of soil cover (sugarcane residue mulch, shading gauze and mosquito gauze) showed that, for a sandy loam soil in the Ivory Coast, soil crusting was directly related to rain kinetic energy. Crust and microlayer development under various combinations of kinetic energy Copyright© Markus Tuller and Dani Or2002-2004
  • 122. The kinetic energy of the rain before runoff occurs is of greatest importance for crusting, since once the surface is covered by a water film the effect of raindrop impact is reduced 2. Irrigation The composition of irrigation water, particularly in respect of its sodicity and electrolyte concentration, determines the ease of chemical dispersion of the soil aggregates. 3. Wind action Wind acts as an agent of erosion. Particles are sorted, transported and deposited by wind. The weakest microlayers of surface crusts, that is, the sandy microlayers of structural type 1 and 2 crusts, are removed by wind and the surface seal exposed, forming an erosion crust. Copyright© Markus Tuller and Dani Or2002-2004
  • 123. V. Consequences of Soil Crusting A. Physical Consequences 1. Infiltration and runoff Fig. Infiltration intensity function of time in a uniform and porous soil as well as in a soil covered with a crust (Musy & Soutter, 1991) Infiltration curves vs. cumulative rainfall during seal formation ... Copyright© Markus Tuller and Dani Or2002-2004
  • 124. The crust rapidly becomes the dominant control on infiltration on most bare soils. The loss in porosity in the surface layer decreases its hydraulic conductivity, so there is a sharp contrast in the hydraulic conductivity of the crust and sub-crust layers. Surface crusting affects 2 characteristics of infiltration: the rate at which infiltration decreases and the final infiltration rate. On soils with good aggregate stability, infiltration decreases more slowly and remains at a greater final infiltration rate. It should be noted that the negative impact of crusting on infiltration can be used positively for water harvesting 60 Infiltration rate (mm/h) Figure shows theoretical curves relating infiltration to aggregate stability. Crusting proceeds more quickly on soils with low aggregate stability, so infiltration rate decreases more rapidly, and the final infiltration rate is lower. 40 Good aggregate stability 20 Intermediate aggregate stability Poor aggregate stability 0 0 20 40 60 80 Cumulative rainfall (mm) 100 Expected changes in infiltration with cumulative rainfall for soils with different aggregate stabilities. Copyright© Markus Tuller and Dani Or2002-2004
  • 125. B. Biological consequences 1. Seedling emergence Hutson (1971) reported on experiments in which the effect of crust strength of a Hutton Shorrocks (Rhodic Paleustalf) soil on the emergence of wheat seedlings was studied. Emergence occurred only when the modulus of rupture was below 400 millibar 2. Agricultural productivity It is usually difficult to assess the contribution of a single soil physical factor to an increase or decrease in crop yields. Surface crusts may adversely affect seedling emergence and water storage in soil and thus influence plant density and crop yield. 5 100 4 Biomass (g) Emergence rate (%) 80 60 40 2 1 20 0 3 1 2 3 WEEK 4 Crust No crust Crusting inhibits emergence of Chloris guyana grass over a 4 week period. 0 Crust No crust Crusting inhibits growth of Chloris guyana grass. Copyright© Markus Tuller and Dani Or2002-2004
  • 126. C. Beneficial Effects of Soil Crusting In arid and semi-arid regions, surface crusting is not invariably detrimental to crop growth since in some areas overland flow can be managed more effectively for agricultural production. Reij et al. (1988) reviewed water harvesting techniques, mainly in Africa's drought-prone zones. •Some of them are very old, such as the terraced wadi systems in southern Tunisia, called "jessour" and described by Bonvallot (1986). •Water is collected from small channels across mountain slopes into earth dams which reduce the flow velocity, increase storage and permit the accumulation of sediments. Thus cereal and tree crops are possible in zones with as little as 100-200 mm annual rainfall. VI. Soil Management for the Prevention Control of Crusting A. -Physical Soil Management 1. Tillage practices Many experiments have shown that conservation tillage practices such as minimum tillage, surface mulching, strip-cropping, contour ploughing etc. will reduce runoff and soil loss (Mallett et al, 1981). For arable agricultural production, tillage is an essential input. Copyright© Markus Tuller and Dani Or2002-2004
  • 127. 2. Mulching It has been shown that mulching results in a rapid regeneration of surface structure (Scholte, 1989), the prevention of surface crusting (Kooistra et al., 1990), and an increase in faunal activity and hence favorable effect on surface crusting. 3. Improving vegetative cover Avoidance of bare soil surfaces will combat crusting. In animal husbandry, it is essential to maintain the environmentally dictated stocking rates. In many areas, a grass ley farming system, among others directed at improving soil aggregation, has been advocated. Several trees or shrubs are thought to improve soil surface structure, e.g. Acacia albida in the Sahel (Dancette and Poulain,1969) and pigeon pea (Cajanus cajan) in the wet savannah zone (Hulugalle and Lal, 1986). 4. Irrigation management On soils highly susceptible to crusting, irrigation systems delivering high kinetic energy drops should be avoided. In the case of overhead irrigation, Valentin and Ruiz Figueroa (1987) insisted that the appropriate sprinkler systems be selected and used at suitable intensities so as to achieve low kinetic energy drops Copyright© Markus Tuller and Dani Or2002-2004
  • 128. B. Chemical Soil Management 1. Use of gypsum/phosphogypsum Gypsum/phosphogypsum is a much vaunted ameliorant to use when sodicity is high or electrolyte concentration is very low 2. Use of soil conditioners: There is no doubt about the ability of synthetic soil conditioners to create stable aggregates. Polyacrylamide (PAM), bitumen and urea formaldehyde were shown to be effective to reduce evaporation from the soil surface. Index of Crusting FAO (1979) proposed an index of crusting (Ic) based on textural composition and soil organic matter content Sf is % fine silt, Sc is % coarse silt, Cl is % clay, and SOM is % soil organic matter content. Obviously, Ic is inversely related to clay and soil organic matter content, and directly to fine and coarse silt content. Copyright© Markus Tuller and Dani Or2002-2004
  • 129. Soil and crop management options for reducing crust formation and minimizing adverse effects on crops Copyright© Markus Tuller and Dani Or2002-2004
  • 130. Soil Puddling Dr. P.K. Mani Department of Agril. Chemistry and Soil Science Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal, India E-mail:, Website:
  • 131. The term puddling was defined by as Buehrer and Rose (1943) “the destruction of the aggregated condition of the soil by mechanical manipulation within a narrow range of moisture contents above and below field capacity (0.3 bars), so that soil aggregates lose their identity and the soil is converted into a structurally more or less homogeneous mass of ultimate particles.” After puddling, a soil is called a puddled soil, defined as a “dense soil with a degraded soil structure; dominated by massive or single-grain structure, resulting from handling the soil when it is in a wet, plastic condition so that when it dries it becomes hard and cloddy.” (Gregorich et al., 2001).
  • 132. Advantages of Puddling: Although puddling, as practiced in much of tropical Asia, involves a great amount of labor, the method has been widely adopted primarily because of its compatibility with other components of production technology and economic conditions, which include: • Improved weed control by primary and secondary tillage through puddling • Ease of transplanting. • Establishment of a reduced soil condition, which improves soil fertility and fertilizer management. • Reduced draft requirements for primary and secondary tillage. • Reduced percolation losses resulting in conservation of water from rainfall action and irrigation completed. • Reliability of monsoon rains by the time puddling operations have been completed (De Datta et al. 1978).
  • 133. During puddling, soils undergo two deforming stresses: normal (load) stress, associated with compression, and tangential stress causing shear. Compression is most effective below the plastic limit, and shearing effects dominate above the upper plastic limit. The work done during puddling can be expressed by Since, puddling is done under saturated condition of soil; it is shear stress which causes dispersion of soil particles in water. Rotary puddler due to rotary motion of its blades matches the weakest fracture plane of soil mass disintegrating it into fine particles (Sharma and De Datta, 1985).
  • 134. Definition of stress and strain The reaction of a solid body to a force F or a combination of forces acting upon or within it can be characterized in terms of its relative deformation or strain. The ratio of force to area where it acts is called stress. normal stress σ = Fn / A shear stress τ = Fs / A normal strain ε = δz / zo shear strain γ = δh / zo Note that compressive stresses and strains are positive and counter-clockwise shear stresses and strains are positive.
  • 135. Apparent Specific Volume of Soil. Change in the apparent specific volume of soil reflects the susceptibility of a soil to puddling. Puddlability is the change in apparent specific volume per unit of work expended. The change in the apparent specific volume of soil is the difference between apparent specific volume after and before puddling (Bodman and Rubin 1948): where ap = after puddling, bp = before puddling. The data are expressed as cm3/g. If the density of water is considered equal to 1 g/cm 3 , which is usual in engineering works (McCarthy 1977), the equation will be where m = mass of water per unit mass of oven-dry soil, or gravimetric moisture content, and Dp = particle density (Bodman and Rubin 1948).
  • 136.  Process of puddling The process of puddling in rice culture is accomplished by a series of tillage operations beginning at soil moisture contents above saturation (i.e.,flooded) and ending at moisture contents closer to field capacity (see Field water cycle). This process is best understood by considering the changes in soil strength within aggregates and between aggregates. According to Koenigs (1961), the cohesion within soil aggregates decreases with increasing soil moisture contents. The individual aggregates become soft and may or may not disintegrate depending on their stability. The cohesion between aggregates is very low at low moisture contents but increases rapidly with increasing moisture, peaking at about field capacity, and decreasing sharply as moisture contents approach saturation. .
  • 137. Maximum puddling occurs at moisture contents between  field capacity and saturation. At such moisture contents, the cohesion within soil aggregates is minimum, so shear planes may easily form. Moreover, when aggregates of dry soil are wetted, uneven swelling and explosion of trapped air also helps form shear planes. At moisture content below saturation, cohesion between the aggregates and clods is maximum, and movement of aggregates along each other and along the implement is therefore restricted. Consequently, the energy of the puddling implement is effectively transferred to shear and destroy the aggregates.
  • 138. The cohesion between aggregates depends primarily on the number of contact points between aggregates. The number of contact points is minimal in a dry soil and approaches a maximum at about field capacity because of the increased thickness of water films and the swelling of the aggregates themselves. At higher moisture contents, the thick moisture films act as lubricants and decrease the number of contact points between aggregates. At approximately field capacity the cohesion within the aggregates is very low and the cohesion between the aggregates is maximum. When force is applied by a plow or a foot, the aggregates are easily destroyed because of the combined effects of high friction and low internal aggregate strength
  • 139. Soils with high cohesion within aggregates, caused by stabilizing agents such as:  Fe and Al hydrous oxides, calcium carbonates, and organic matter, need a larger energy input for puddling.  High clay content favors puddling, but kaolinitic clays are more difficult to puddle than montmorillonite clays. Similarly, Na–saturated clays puddle more easily than Ca–saturated clays. Andepts and Oxisols are extremely difficult to puddle, and the degree of aggregate breakdown seems lower than in other soils.
  • 140. Consequences of puddling (i) Aggregate destruction The primary consequence of puddling is the destruction of soil aggregates (Sharma and De Datta, 1985). A puddled soil consists essentially of a two-phase or solid-liquid system. Individual clay particles or clusters thereof are oriented in parallel rows and are surrounded by capillary pores saturated with water. Sand and silt particles and some remaining aggregates are also part of the matrix. The degree of aggregate destruction is difficult to quantify because drying is necessary to measure aggregation. Kawaguchi et al. (1956) and others provide evidence of aggregate destruction after puddling and subsequent drying.
  • 141. (ii) Changes in porosity Non capillary pores are essentially eliminated in the process of puddling. Bodman and Rubin (1948) found that 91–100% of the volume occupied by such pores was destroyed by puddling a silt loam. Capillary porosity increases drastically. Because most of these pores are smaller than 0.2 mm in effective radii, water may move through pores as a liquid but can be lost only was vapor. (iii) Bulk density Immediately after puddling a saturated soil, the apparent specific gravity or bulk density is less than that of the original soil because of the larger total pore volume occupied by water. With time, however, the bulk density of the flooded soils increases probably because of a slow settling of the clays. When dried, puddled soils shrink dramatically with resultant large increases in bulk density ( Sanchez, 1968).
  • 142. (iv) Increased soil moisture retention As a consequence of the destruction of noncapillary pores, the increase in water-saturated capillary pores, and the decrease in initial bulk density, puddled soils hold more water than unpuddled soils at a given moisture tension. The effect is measurable within a range of 0 to 10 bars of soil moisture tension. (V) Decreased moisture losses The changes in porosity and water retention result in sharply reduced soil moisture loss patterns in puddled soils (Sharma and De Datta, 1985). Puddling decreased percolation losses by a factor of 1000 regardless of soil properties.
  • 143. Reducing conditions Due to the absence of air, reduction processes can take place as soon as the soil is puddled (Breazeale and McGeorge,1937). Puddled soils remain reduced regardless of whether they are flooded until cracks begin to form. Lack of oxygen in the soil pores inhibits the growth of most crops except rice and other anaerobic species. Nitrates are lost through denitrification (Aggarwal, 1995). Organic matter decomposition Puddling, like any other aggregate disruption process, temporarily hastens organic matter decomposition due to increased accessibility of the substrate by soil microorganisms. Puddling increases the mineralization of soil organic nitrogen during the first month after puddling and flooding (Harada et al., 1964), but the effect disappears at later stages (Briones, 1966).
  • 144. Nutrient availability Puddling flooded soils does not directly increase the availability of nutrients to the rice plant (Sanchez,1973)  Small increases in iron and manganese availability have been recorded (Naphade and Ghildyal, 1971) but are not large enough to be of practical significance. Puddling often indirectly increases the availability of nutrients by decreasing leaching losses of cations such as NH4+ Effects of puddling on crop growth: The effects of puddling on crops other than rice are clearly detrimental (McGeorge and Breazeale, 1938). For rice, puddling is considered advantageous because it facilitates land leveling, permits the farmers to work the soil regardless of moisture status, reduces initial weed infestations, and, most important, decreases water and leaching losses.
  • 145. Regeneration of structure Puddling is not an irreversible process. The original structure can be regenerated through the processes of alternate wetting and drying or freezing and thawing. The puddled soil must be dried first, after which aggregates are reformed by these processes. Tillage at the appropriate moisture content facilitates regeneration of structure. This is accomplished most readily in soils high in organic matter or iron and aluminum oxides (Koenigs, 1961). Briones (1977) concluded that montmorillonitic clay soils with low organic matter and iron oxide contents are more difficult to convert from lowland to dryland use than kaolinitic clay with higher organic matter and iron oxide contents. This indicates that incorporation of crop residues aids regeneration of soil structure.
  • 146. Puddling, however, is a double-edged sword in rainfed paddy systems. In most cases puddling attenuates the increases in soil moisture tension during temporary droughts and increases yields. But when intense droughts take place shortly after transplanting, the puddled soil may shrink, crack, and impede rice root development to a degree from which plants cannot recover afterwards (Sanchez, 1973; De Datta and Kerim, 1974). Another potential detrimental effect of puddling is the time required for the soil to dry and be prepared for aerobic crops grown in rotation with rice. This time interval may be several months in clayey montmorillonitic soils but only several days in clayey kaolinitic, allophanic, or oxidic soils. In continuous paddy rice systems, this effect is irrelevant.
  • 147. Drying of the puddle soil leads to formation of cracks, which may have an adverse impact on root growth of rice seedlings.
  • 148. • Puddling and subsequent flooding differentiate lowland rice soils chemically and pedologically from other arable soils. • An important difference between a dryland and a puddled lowland soil is the presence of the reduced soil layer in the puddled soil system. •The puddled layer is divided into several subhorizons. • The formation of relatively impermeable layers, or plow pans, is attributed to physical compaction (at the same depth) during puddling, and to eluviation of clays and reduced iron and manganese. • The plow pan is found in loamy soils that have grown rice for many years and in well drained Latosols, but is absent in clayey soils, Vertisols, young alluvial, and calcareous soils (Moormann and Dudal 1964).
  • 149. Long-term effects of puddling Long–term puddling forms a hardpan in the subsoil below the puddled layer. It may take 3 to 200 yr for a hardpan to form, depending on soil type, climate, hydrology, and puddling frequency (24). Subsurface hardpans develop from physical compaction and precipitation of Fe, Mn, and Si. Compact, 5– to 10–cm thick layers which occur in low land rice soils between 10 and 40 cm depth and that have higher (dry) bulk density and lower total porosity and water permeability than the over- and underlying soil horizons were called plow pans by Koenigs (in 24) and traffic pans by Moormann and van Breemen
  • 150.  Chemically cemented pans are formed in the oxidized subsoil, usually 15 to 20–cm deep, by precipitation of Fe, Mn, and Si from upper, reduced soil layers.  Soils with slowly permeable subsurface horizons, oxidized subsoils, low pH, high concentrations of easily reducible Fe and Mn, and easily decomposable organic matter favor chemical precipitation. Because continuously submerged soils have excessively reduced conditions, Fe– and Mn–pans form very slowly. Under favorable conditions, Mn– and Fe–pans may develop in 8–40 yr. Ferrolysis (4) is another long–term effect of puddling that may lower soil productivity.
  • 151. Puddling index: The puddling index is the ratio of the volume of settled soil to the total volume of soil sample and is expressed as a percentage. Where, PI = puddling index in per cent, Vs = volume of settled soil and Vt = total volume of soil sample. A higher value of puddling index indicates the better quality of puddling
  • 152. Soil Tilth • Soil tilth is the workability of the soil based on texture, structure and some other factors • Soil moisture and compaction play a role • Often due to over-working the soil and preventing root penetration Soil tilth is defined as “ the physical condition of a soil as related to its ease of tillage, fitness as a seedbed, and its importance to seedling emergence and root penetration ” (SSSA, 1979). Copyright© Markus Tuller and Dani Or2002-2004
  • 153. Tilth index Tilth index was calculated using the model developed by Singh et al. (1992) and a new model developed from the regression of crop yields on soil physical properties. The model proposed by Singh et al. (1992) utilizes bulk density, cone index, organic matter content, aggregate uniformity coefficient, and plasticity index as parameters for deriving tilth index. Since in puddled soil, aggregates are broken down, the aggregate uniformity coefficient in rice plots does not carry any significance, and the cone index could not be reliably obtained during the wheat season in unsaturated soils due to high clay content (>30%). Therefore, only bulk density, organic matter content, and plasticity index were included in the model for determining the tilth index for rice and wheat. Singh et al. (1992) indicated that the number of properties used in calculating tilth index could be varied.
  • 154. According to the model of Singh et al. (1992), the tilth index is a multiplicative combination of tilth coefficients expressed as where TI is the tilth index (0.0 ≤ TI ≤ 1.0), CF the tilth coefficient, and n the number of soil properties used for calculation of the tilth index. The limiting, critical and non-limiting values of tilth coefficients assigned by Singh et al. (1992) for the soil properties, to simulate the Neill’s sufficiency curve are given in Table 1.
  • 155. The proposed regression model is based on multiple linear regression of crop yield on pertinent soil physical properties as Y = a + b1X1 + b2X2 +· · ·+bnXn (2) where Y is the grain yield of the crop, X1, X2, . . . ,Xn are the different soil properties, and a, b1, b2, . . . , bn are constants. Those physical properties whose coefficients (b1, b2, . . . , bn) in Eq. (2) were found significant by t-test were selected for calculating the tilth index.
  • 156. These selected physical properties were then individually subjected to linear regression with yields of rice and wheat and their coefficients of determination (R2) were obtained. The proportionate variation of R2, obtained from the linear regression of the selected properties on yield, was then expressed as Ai ,
  • 157. The soil tilth index (TI), as originally developed by Singh et al where TI is the soil tilth index (0.0 ≤ TI ≤ 1.0), CF1 to CF5 are the tilth coefficients of bulk density, cone index, plasticity index, aggregate uniformity coefficient,and organic matter content, respectively. Singh et al.proposed a quadratic relationship for the tilth coefficients for each soil factor. The proposed general form of equation was: Copyright© Markus Tuller and Dani Or2002-2004
  • 158. where CFx is the tilth coefficient for the soil property (X) and A0, A1, A2 are empirical constants. Singh et al.3 derived this relationship simply by examining each soil factor separately according to defined criteria. The defined criteria in each case involved setting three important levels for each soil property that were critical in the growth of a crop. These were non-limiting (sufficient level), critical and limiting points. The nonlimiting condition is the optimal level for maximum plant growth, while the limiting level is the level above which the plants will not normally survive8. These values were then plotted on a graph and the best fitting polynomial curve determined to define a regression equation to establish other values within the range. The tilth coefficients were normalized to range between 0and 1, so that a tilth index of 0 indicated an absolutely limiting level of a soil property and a value of 1 indicated the optimum level. Copyright© Markus Tuller and Dani Or2002-2004
  • 159. MECHANICAL IMPEDANCE Mechanical impedance occurs where soil is lacking in pores of appropriate size for roots or shoots to grow through, and/or is too hard for the growing root or shoot to push out of the way. A root must be able to enlarge existing pores, or create new pores, to elongate through the soil. It seems probable that root hairs (which are involved in nutrient uptake) can only grow into pre-existing pores which are of the same or greater diameter than they, i.e. >= 10 μm dia. growth in a soil with no a. Root mechanical impedance problems; b. Root growth in a soil with prismatic structured subhorizons. Vertical root extension is restricted to the cracks between the clay structures; c. Root growth above a compacted subsoil. Vertical extension is hindered but restricted drainage causing aeration problems may also be a factor Copyright© Markus Tuller and Dani Or2002-2004
  • 160. Copyright© Markus Tuller and Dani Or2002-2004
  • 161. Importance of soil conditioners/Amendments under INM Copyright© Markus Tuller and Dani Or2002-2004
  • 162. Importance of soil conditioners/Amendments under INM Introduction • A soil conditioner, also called a soil amendment, is a material added to soil to improve plant growth and health. • The type of conditioner added depends on the current soil composition, climate and the type of plant. • A conditioner or a combination of conditioners corrects the soil's deficiencies. • Fertilizers, such as peat, manure, anaerobic digestate or compost, add depleted plant nutrients. • Gypsum releases nutrients and improves soil structure. Copyright© Markus Tuller and Dani Or2002-2004
  • 163. Importance of soil conditioners/Amendments under INM Characteristics of soil conditioners • • • Soil conditioners are natural and earthy. Absorb water rapidly. Compost is “Synthetic manure made from decomposing materials, fertilizer and soil. • Leaves and manures are also natural products. Copyright© Markus Tuller and Dani Or2002-2004
  • 164. Importance of soil conditioners/Amendments under INM Functions of soil conditioners • • • • They help to improve the amount of minerals in the soil. Soil that is rich in minerals will produce much healthier vegetation. Leaves work by attracting earthworms which create a healthy soil . Soil improved by • • • Physical Chemical Biological Copyright© Markus Tuller and Dani Or2002-2004
  • 165. Importance of soil conditioners/Amendments under INM Importance of soil conditioners • Soil conditioner is a product which is added to soil to improve the soil quality. • Soil conditioners can be used to rebuild soils which have been damaged by improper management, to make poor soils more usable, and to maintain soils in peak condition. • A wide variety of products can be used to manage soil quality, with most being readily available from nurseries and garden supply stores. • People can also generate their own soil conditioner with materials from home. Copyright© Markus Tuller and Dani Or2002-2004
  • 166. Importance of soil conditioners/Amendments under INM Importance of soil conditioners • Many soil conditioners are designed to improve soil structure in some way. • Soils tend to become compacted over time, which is bad for plants, and soil conditioners can add more loft and texture to keep the soil loose. • They also add nutrients , enriching the soil and allowing plants to grow bigger and stronger. • Soil conditioners improve the water retention in dry, coarse soils which are not holding water well, and they can be added to adjust the PH of the soil to meet the needs of specific plants or to make highly acidic or alkaline soils more usable. Copyright© Markus Tuller and Dani Or2002-2004
  • 167. Importance of soil conditioners/Amendments under INM Soil physical conditions and soil conditioners • Soil physical condition is one factor that can limit crop production. • Poor soil physical condition can restrict water intake into the soil and subsequent movement, plant root development, and aeration of the soil. • These goals can be accomplished in part through the use of good management techniques. • Producers and researchers alike are interested in improving the physical condition of the soil and, thus, enhance crop production. Copyright© Markus Tuller and Dani Or2002-2004
  • 168. Importance of soil conditioners/Amendments under INM Vital role of soil conditioners • • • • • • • • • • Improved soil structure and aeration Increased water-holding capacity. Increased availability of water to plants Reduced compaction and hardpan conditions. Improved tile drainage effectiveness Alkali soil reclamation Release of “locked” nutrients Better chemical incorporation Better root development Higher yields and quality Copyright© Markus Tuller and Dani Or2002-2004
  • 169. Importance of soil conditioners/Amendments under INM Role of Soil Conditioner • Soil conditioners may be used to improve water retention in dry, coarse soils which are not holding water well, and they can be added to adjust the pH of the soil to meet the needs of specific plants or to make highly acidic or alkaline soils more usable. Examples of soil conditioners • Peat • Compost • Coir • Manure • Straw • Vermiculite etc., Copyright© Markus Tuller and Dani Or2002-2004
  • 170. Types and use of soil conditioners/amendments under INM Types Organic soil conditioners Inorganic (Synthetic) soil conditioners Copyright© Markus Tuller and Dani Or2002-2004
  • 171. Types and use of soil conditioners/amendments under INM Types of Organic soil conditioners Organic Green Manure Compost Peat Crop Resides Coconut shell mulch Copyright© Markus Tuller and Dani Or2002-2004
  • 172. Types and use of soil conditioners/amendments under INM Types of Inorganic soil conditioners Inorganic Synthetic Binding Agents Mineral Conditioners Gypsum Copyright© Markus Tuller and Dani Or2002-2004