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PROPERTIES OF SAND Vs. SILT Vs. CLAY
SAND
    1) Physical - structurally simple; relatively unweathered, physically broken down parent material

    2) Chemical- relatively inert; results in:
        a) little effect on soil chemistry and pH 
        b) poor nutrient holding capacity (i.e. CEC)

    3) Pore Space
        a) less total pore space
        b) more large (macro) pores, fewer small (capillary) pores; thus sand causes:
            1) increased aeration
            2) increased drainage
            3) decreased water holding capacity
 

SILT - intermediate chemical and physical properties between sand and clay 
 

CLAY
    1)Physical - structurally complex
        a) colloidal - sub-microscopic and held in suspension in solution
        b) when wet - viscous and gelatinous, sticky; when dry - hard, packed and cohesive
        c) composed of micelles = flat, sheet-like plates laminated into stacks
        d) very large internal and external surface area 
        e) very small internal and external pores

    2) Chemical - very complex; negatively charged
        a) very high cation exchange capacity (CEC); hence, nutrient holding capacity
        b) charge allows flocculation (aggregation) or de-flocculation (spread-out)
            1) Ca+2 promotes flocculation of soil particles, and good soil structure
            2) Na+ promotes de-flocculationof soil particles, and good soil structure

    3) Pore Space
       a) greater total pore space
        b) more small (capillary) pores; fewer large (macro) pores; thus clay causes:
            1) decreased aeration 
            2) decreased drainage
            3) increased water holding capacity
            4) but not all water is available 
 

TYPICAL AGRICULTURAL SOIL
An agriculturally productive soil is a balanced mixture of sand, silt, and clay. For example, a typical loam soil is composed of 40% sand, 40% silt, and 20% clay. This yields a balance between aeration vs. drainage vs. water holding capacity vs. fertility.