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Basic of Soil Science

Soil science is the study of soil as a natural resource, focusing on its formation, classification, mapping, physical, chemical, biological properties, and its role in supporting plant growth. It encompasses various sub-disciplines such as pedology (study of soil formation and distribution), edaphology (study of soil's effect on plant growth), and soil fertility management. Soil scientists examine soil texture, structure, moisture, and nutrient content, as well as its interactions with water, air, and living organisms. The knowledge gained through soil science is crucial for agriculture, land

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Basic of Soil Science

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  1. SoilScience

  2. Three spheres, correspondingtothethree statesof matter(solid, liquid and gas) constitute the earth. • Thesolidzoneis • lithosphere • Land which is covered by water forming seas and oceansisthe hydrosphere • Thegaseousenvelopeover the earth’ssurface isthe atmosphere.

  3. Pedology: Formation, chemistry,morphology and classification of soil) • Edaphology: Influence of soil on organisms,especially plants.

  4. WhatisLand &Soil? Land is broadly defined as total natural environmentoftheareasoftheearthnot coveredbywater. In addition to soil, its attributes include all thelivingorganisms,theairandwaterbodies withinoronitandrocksbelow. Solumwhichmeans floororground. Asoil scientist call soil, a geologist may call fragmentedRockAndEngineeringmaycall earthandeconomicmaycallland.

  5. ConceptofLandandSoil

  6. Componentof Soil

  7. Rocks

  8. Formation ofrocks 1. Cooling and consolidation of molten magma withinoron the surfaceofearth 2. Transportation and cementationof primaryrocks 3.Alteration of theexisting primaryand secondaryrocks

  9. Geologistshave classifiedrocksinto three majorgroups Igneous Sedimentary Metamorphic

  10. Weathering • Weathering is the process of transformation of solid rocks into parent material orRegolith.

  11. Weathering happens throughthree major ways, namely: • PhysicalWeathering • Chemicalweathering • BiologicalWeathering

  12. The soil formation is the processoftwoconsecutive stages. SoilForming Factors 1.Theweatheringofrock (R)intoRegolith 2.Theformationoftrue soilfromRegolith

  13. Fundamental Soilforming Processes • Eluviation: It is the mobilization and translocationofcertainmineralsinthesoil. • Eluviation means washing out. It is the process of removal of constituents in suspension or solution by the percolating waterfromtheuppertolowerlayers.

  14. Illuviation: The process of deposition of soil materials (removed from the eluvial horizon)inthelowerlayer(orhorizonof gains having the property of stabilizing translocated clay materials) is termed as Illuviation. • Bhorizonreferstothezoneof illuviation.

  15. Primary Mineralsin soil Theminerals inthesoil areclassified into two categories: Secondary Mineralsin soil

  16. ImportantSoilProperties Drainage Depth Available WaterHolding Capacity Infiltration Reaction Cation Exchange Capacity Landscape Position

  17. Soiltexture • Soiltexturereferstotherelative proportion of particles or it is the relative percentage by weight of the three soil separates viz.,sand,silt and clay. • Theproportionofeachsizegroup in a given soil (the texture) cannot be easily altered and it is consideredasabasicpropertyof a soil.

  18. Accordingto theInternationalsystem of soilclassification,sizeof different particleareas follows • Size of The Particles (In SoilTexture) • Particlesizeis determinedbythe diameter of individual soilfragments.

  19. ClassificationbyUSDA

  20. ClassificationbyISSS

  21. Soiltextural classes • Toconveyanidea of the textural make up of soils and to give an indication of their physical properties, soil textural class namesareused.

  22. Soilstructure • The arrangement and organization ofprimaryandsecondaryparticles ina soilmass isknownassoil structure. • Soilconditionsand characteristics such as water movement, heat transfer, aeration, and porosity are muchinfluencedbystructure.

  23. 3. Granular and crumbysoilstructures • aremostlyfoundin • whichhorizon? • A. B-Horizon • •BB..AA--HHoroirzioznon • C.R-Horizon • D.CHorizon

  24. EffectofSoilStructureonotherPhysicalProperties Porosity Temperature Consistence Root penetration Colour

  25. Soilstructureinfluencesthe amountand nature of porosity. • Structurecontrols the amountofwaterandairpresent in the soil. Not only the amount of water and air dependent on soilstructure,but theirmovementand circulationare alsocontrolled bysoilstructure. • Itaffectstillagepractices. • Structurecontrolsrunoffanderosion. • Platystructurenormallyhindersfreedrainage whereasspherelikestructure(granularandcrumby) helps in drainage. • Crumbyandgranularstructureprovidesoptimum infiltration,waterholding capacity,aerationand drainage.Italsoprovidesgoodhabitatfor microorganismsand supplyof nutrients. The role of soil structurein relation to plantgrowth

  26. 4. What is the particledensity • ofsiltsoil? • A.2.655 • B.2.837 • •CC..22..779988 • D.2.659

  27. Consistence • Soilconsistenceisdefinedas“the resistanceofasoilat variousmoisture contentstomechanicalstressesor • manipulations” • Itcombinesboththe‘cohesive’and ‘adhesive’forces,whichdeterminethe easewithwhicha soilcanbereshaped orruptures.

  28. Consistence Plasticityisthedegreeto whichareworkedsoilcan bepermanentlydeformed withoutrupturing. Plasticityisevaluatedby forminga roll(wire)ofsoil thatis4cmlong. Theplasticityindex(PI)is ameasureoftheplasticity ofasoil.

  29. Bulkdensity andparticledensityofsoils& porosity • ParticleDensity:Theweightperunitvolumeofthesolidportion ofsoil iscalledparticle density. • Generallyparticledensityofnormalsoilsis2.65gramspercubic centimeter. • Theparticledensityishigher iflargeamountofheavyminerals such asmagnetite,limoniteandhematiteare presentinthe soil. • Particledensityisalsotermedastrue density.

  30. Importantdata

  31. BulkDensity • The oven dry weight of a unit volume of soil inclusive of pore spaces is calledbulkdensity. • The bulkdensityofasoilisalwayssmaller thanitsparticledensity. • As aruleof,mostrockshave adensityof2.65 g/cm3soideally,asilt loamsoilhas50%porespaceandabulkdensityof1.33g/cm3. • The bulkdensityof sandysoilisabout1.6g/ cm3,whereasthat of organicmatterisabout0.5. • Bulkdensitynormallydecreases,asmineralsoilsbecomefiner in texture.

  32. Thebulkdensityvariesindirectlywiththetotal pore space present in the soil and gives a good estimateof theporosityof thesoil. • Bulk density is of greater importance than particle density in understanding the physical behavior of thesoil. • Generallysoils with low bulkdensitieshave favorablephysicalconditions.

  33. Bulkdensityof different texturalclasses

  34. Porosity • Soilporosity refersto thatpartofasoil volumethatisnotoccupied bysoil particlesororganic matter. • In sandysoils,the particlesarearranged closelyandtheporespaceis low.Inclaysoils,theparticlesarearrangedaswell aggregatesand theporespaceishigh. • Presenceoforganicmatterincreasesthepore space. • Virginsoils have moreporespace • Conservation tillage andnotillagereducesporositythan conventional tillage

  35. 1.Macropores(non-capillarypores): diameter>0.05mm • 2.Micropores(capillarypores):diameter • <0.05mm • In macro pores, air and water moves freely due to gravitation and mass flow. In micro pores,themovementofairandwaterisvery slow and restricted to capillary movement anddiffusion. • Sandysoilhavemoremacroporesand claysoilshavemoremicro pores. • So insandysoils,waterandairmovementis rapid due to macro pores though the pore space is higher and in clay soils the air and water is slower due to micro pores though thetotalporespaceishigher. Sizeof pores

  36. Calculatethe%porosity

  37. %porosity= Formula to calculate Porosity 100 - (bulk density/particle density)x100

  38. Whichsoilshowsthe characteristic of shrink swell Potential? • A•A..BBllaacckkssooilil • B.RedSoil • C.Alluvialsoil • D.Dessertsoil

  39. Shrink-swellpotentialisa measurementoftheamount ofvolumechangethatcan occur when a soil wets and dries. • Mostofthisvolumechange isduetotheclay fractionof thesoil. • Claysswellwhenwetand shrinkwhen dry. • Montmorillonitetendto havehighshrink-swell potentials. • Andkaolinitetendtohave lowshrink-swellpotentials. Shrink-swellPotential

  40. Shrink-swell Potential

  41. Drainage • Drainage refers to the frequency and duration of periods of saturationorpartialsaturation. • Internalsoildrainage is important becauseofitseffect onlanduseand managementdecisions.

  42. Entryof Water intoSoil

  43. The movement andfiltrationof water through soils and permeable rock is termedas Percolation

  44. Thecapacityofsoils to hold water available for use by most plants. • It is commonly defined as the differencebetween the amount of soil water at field capacity and the amount at wilting point. AvailableWaterHolding Capacity

  45. Classesandavailabilityofsoilwater Gravitational water: Capillary water: Hygroscopic water: Hygroscopic coefficient Waterheld by surface tension in the pore spaces. Waterheld tightly to the surface of thegrainsby adsorption. Water moves freely in responseto gravity. Soil moisture decreased to wiltingpoint water held tightly by soil particles

  46. Gravitational<0.3ATM or-1/3bar CapillaryWater: 0.3-31ATM(0.3-15ATM) or-1/3to-31 bars Hygroscopic:>31ATM (31-10000ATM)or -10,000bars 1atm= 1.01325bar

  47. Soilmoisture constantsandrangeof tension Moistureclass Tension (atm) pF Hygroscopic Hygroscopic coefficient Wilting point Capillary Fieldcapacity Gravitational 31 to10,000 4.50to7.00 31 4.50 15 4.20 1/3 to31 2.54to4.50 1/3 2.54 Zeroorlessthan1/3 <2.54

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