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Concept
Pore space in soil
Summary
The pore space of soil contains the liquid and gas phases of soil, i.e., everything but the solid phase that contains mainly minerals of varying sizes as well as organic compounds.
In order to understand porosity better a series of equations have been used to express the quantitative interactions between the three phases of soil.
Macropores or fractures play a major role in infiltration rates in many soils as well as preferential flow patterns, hydraulic conductivity and evapotranspiration. Cracks are also very influential in gas exchange, influencing respiration within soils. Modeling cracks therefore helps understand how these processes work and what the effects of changes in soil cracking such as compaction, can have on these processes.
The pore space of soil may contain the habitat of plants (rhizosphere) and microorganisms.
Bulk density
The bulk density of soil depends greatly on the mineral make up of soil and the degree of compaction. The density of quartz is around 2.65 g/cm3 but the bulk density of a soil may be less than half that density.
Most soils have a bulk density between 1.0 and 1.6 g/cm3 but organic soil and some friable clay may have a bulk density well below 1 g/cm3.
Core samples are taken by driving a metal core into the earth at the desired depth and soil horizon.
The samples are then oven dried and weighed.
Bulk density = (mass of oven dry soil)/volume
The bulk density of soil is inversely related to the porosity of the same soil. The more pore space in a soil the lower the value for bulk density.
Porosity
or
Porosity is a measure of the total pore space in the soil. This is measured as a volume or percent. The amount of porosity in a soil depends on the minerals that make up the soil and the amount of sorting that occurs within the soil structure. For example, a sandy soil will have larger porosity than silty sand, because the silt will fill in the gaps between the sand particles.
Hydraulic conductivity (K) is a property of soil that describes the ease with which water can move through pore spaces.
Official source
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