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2.3 Biological Characteristics
When we want to assess biological activity in
a soil, a good measure is the respiration rate
or the rate at which the soil emits carbon
dioxide. Most of the organisms discussed
above have metabolisms just like those that
live aboveground, breathing or otherwise
consuming oxygen and producing CO
2
.
Respiration allows us to gauge how active
the soil ecosystem is, even though we cannot
observe this activity directly because so many
soil organisms are too small to see without a
microscope.
Soil respiration describes the rate at which
soil organisms are consuming soil organic
matter. Respiration rates that are high indicate
that soil organisms are active and either soil
organic matter is being converted to more
stable compounds (e.g. humus) or that carbon
is lost into atmosphere as CO
2
, depending on
plant little input quality and soil management.
During respiration, soil organisms free up
nutrients, such as nitrogen and phosphorus
that are bound in organic matter, and make
them available to other organisms. A low
respiration rate indicates lack of biological
activity in the soil ecosystem.
Soil respiration rates vary dramatically with
a soil’s moisture content, and thus we can
expect seasonal and daily variability and
variability between areas with different
climates. As most microbial activity in the
soil occurs around or in water, respiration
increases with moisture, but only up to the
amount of water that limits air movement
through soil pores. Soil respiration also
generally increases with higher temperatures.
There are several methods for measuring
respiration rate, including commercially
available kits with chemicals that change
color to indicate the amount of CO
2
that is
produced over time in an enclosed space
like a jar.
Soil Respiration