Recognizing Soil Texture & Structure

Student Learning Objectives After this lesson students will be able to: Distinguish sand, silt and clay soil particles. Use the soil texture triangle to determine soil textures. Describe the texture of soil particles.

PS U6 L4

Soil Texture Soil texture = proportions of sand, silt and clay Property of the soil controlled by the size of individual grains or particles

Soil Texture 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 Soil Textures Sand Silt Clay

Fine Textured Soils Clay Sandy Clay Clay Loam Silty Clay Silty Clay Loam

Medium Textured Soils Sandy Clay Loam Loam Silt Loam Silt

Coarse Soils Sand Loamy Sand Sandy Loam

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)

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

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

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

Platy Structure Soil aggregates developed along the horizontal direction: flaky

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

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

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

Types of Soil Structure Angular Blocky: Block-like – three dimensions of same magnitude Subangular blocky: same as angular except the vertices are more rounded

Good Soil Structure Good Soil Structure:

Good Soil Structure Good Soil Structure: Necessary for good water penetration into the soil Water holding capacity Ease of working the soil

Good Soil Structure Good root penetration Favorable movement of soil air Availability of plant nutrients Good internal drainage

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

What questions do you have?