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2.1 Physical Characteristics
Pore space is affected by the amount of clay
and organic matter a soil contains, which
are key in aggregating solid soil particles and
thus making space for air or water. There are
two types of pore space in soils, and every
soil likely has a mix of both.
When thinking about pore space, it is important to consider not only the total collective amount of
pore space throughout a soil, but also the size of individual pore spaces. Keep in mind the different
behaviors of water and air in macropores compared with their behaviors in micropores.
Pore Space
Glossary
Pore Space
part of the soil that is either air or water.
Macropores
are generally greater than 0.08 mm in
diameter. They are related to increasing soil
organic matter and aggregation, as well as to
the activity of soil organisms and roots. They
can also form between sand grains, which
gives sandy soil its well-drained and aerated
property.
•
Increasing macropores leads to
increased water and air movement.
Micropores
are generally less than 0.08 mm in diameter.
They are largely formed in clayey soils and
are characterized by slow air and water
movement.
•
Micropores are usually filled with water,
but this water is not available to plants
because it is held too tightly.
•
And they are too small to allow much
air movement.
Discussion – Pore Size Distribution
What management activities might cause a relative decrease in macropores
and a relative increase in micropores?
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