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2. Soil Fundamentals
Water holding capacity
The amount of water that is available to plants is also related to water holding capacity, which
in turn is related to soil texture.
The same processes of draining and drying out occur in all soil types but can take different
amounts of time. Think of a water droplet moving from the top to the bottom of each panel
in the pore space figure (page 30) and how much longer and more tortuous one soil would
be compared to the other. Different soils hold different amounts of water and therefore have
different water holding capacities.
Note: For a given soil texture class, compaction and salt accumulation will further reduce water
holding capacity.
Organic matter can directly and indirectly increase water holding capacity. Organic matter holds
more water than a similar volume of mineral soil, but can hold it more tightly (like clay). Organic
matter also improves soil structure, which in turn can affect water holding capacity by increasing the
size of pore spaces.
Glossary
Water Holding Capacity
the amount of water that is in the soil
between field capacity and the permanent
wilting point.
Texture class (see “Soil
Texture Class”, page
21)
Water holding capacity
(inches of water per
foot depth)
Soil water behavior
Coarse sand
0.25 to 0.75
Drains very quickly
Loamy Sand
1.1 to 1.2
Drains moderately quickly
Silt Loam
2 to 2.5
MOST available to plants
Silty Clay
1.5 to 1.7
Held moderately tightly
Clay
1.2 to 1.5
Held very tightly