Teaching Organic Farming and Gardening

Soil Physical Properties

20 | Unit 2.1

c) Properties influencing permeability

i. Texture

Soil texture is usually the dominant soil property affecting infiltration. Soils that are
high in clay content tend to have a slower permeability. Soils that are high in sand

content tend to have a faster permeability (see Table 6).

tabLe 6. SOIL PERMEABILITy CHART

THESE ARE NORMAL VALUES FOR NON-COMPACTEd SOILS, SUCH AS IN GRASSLANd SITUATIONS

textUre cLass textUre perMeabiLity rate perMeabiLity cLass

Coarse gravel, coarse sand > 20 inches/hour very rapid

sand, loamy sand 6 – 20 inches/hour rapid

Moderately Coarse coarse sandy loam 2 – 6 inches/hour moderately rapid
sandy loam
fine sandy loam

Medium very fine sandy loam 0.60 – 2 inches/hour moderate
loam
silt loam
silt

Moderately fine clay loam 0.20 – 0.60 inches/hour moderately slow
sandy clay loam
silty clay loam

Fine sandy clay 0.06 – 0.20 inches/hour slow
silty clay
clay (<60%)

Very fine clay (>60%) < 0.06 inches/hour very slow
clay pan

Soil texture not only affects how fast water moves through the soil, it also affects the
pattern by which water moves through the soil. Water will move almost straight down

through a sandy soil, whereas it will have more lateral movement in a heavier soil (one

with more clay). (See figure 5)

figUre 5. MOVEMENT OF WATER THROUGH SANdy ANd CLAy SOILS

Students’ Lecture Outline

Sandy loam clay loam

distance    from    furrow  center  (inches)

distance    from    bottom  (inches)