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Recognizing Soil Texture & Structure

Recognizing Soil Texture & Structure. Soil Texture. Soil texture = proportions of sand, silt and clay Property of the soil controlled by the size of individual grains or particles Soil is usually made up of particles of widely varying sizes.

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Recognizing Soil Texture & Structure

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  1. Recognizing Soil Texture & Structure

  2. Soil Texture • Soil texture = proportions of sand, silt and clay • Property of the soil controlled by the size of individual grains or particles • Soil is usually made up of particles of widely varying sizes. • Soil texture expresses the average or combined effect of all these grain sizes

  3. 3 Soil Textures • Sand • Silt • Clay

  4. Feel that soil! • Sand: In the moist condition sand should feel gritty and will be loose and single grained. Squeezed when wet, it will fall apart when the pressure is released • Clay: when moist is quite plastic and sticky when wet. When the moist soil is squeezed out between the thumb and fore finger, it will form long flexible ribbons. • Silty Soil: when dry and pulverized will feel soft and floury. When wet the soil readily runs together and puddles. When squeezed between the thumb and finger it will ribbon but the ribbon will appear checked and cracked.

  5. Fine Textured Soils • Clay • Sandy Clay • Clay Loam • Silty Clay • Silty Clay Loam

  6. Medium Textured Soils • Sandy Clay Loam • Loam • Silt Loam • Silt

  7. Coarse Soils • Sand • Loamy Sand • Sandy Loam

  8. Soil Structure the combination or arrangement of primary soil particles into secondary particles, units, or peds (which are separated from adjourning aggregates by surfaces of weakness)

  9. Soil Aggregation The cementing or binding together of several soil particles into a secondary unit, aggregate, or granule **clods are different – they are caused by some disturbance such as plowing or digging

  10. Consistence The resistance of a material of deformation or rupture – the degree of cohesion or adhesion of the soil mass

  11. Structureless soil Soil where the particles of coarse soil fail to cling together, when fine soil breaks into large clods, or when the soil is massive, a single compacted substance

  12. Platy Structure Soil aggregates developed along the horizontal direction: flaky

  13. Prismatic Structure A soil structure type with a long vertical axis that is prism shaped, vertical faces are well defined, without rounded caps

  14. Columnar Structure Vertically oriented, round-topped structural prisms – rounded caps

  15. Granular Structure A natural soil ped or aggregate – have plane or curved surfaces which have slight or no accommodation to the faces of surrounding peds

  16. Types of Soil Structure • Platy • Prismatic • Columnar • Angular Blocky: Block-like – three dimensions of same magnitude • Subangular blocky: same as angular except the vertices are more rounded • Granular • Crumb: similar to granular except the peds are porous

  17. Class of Structure Size of individual ped

  18. Good Soil Structure • Good Soil Structure: • Necessary for good water penetration into the soil • Water holding capacity • Ease of working the soil • Good root penetration • Favorable movement of soil air • Availability of plant nutrients • Good internal drainage

  19. Binding Agent in the soil • Organic matter converted to humus is the chief binding agent for stable soil structure. • Continuous cultivation and never plowing under any organic matter tends to destroy structure

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