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.
or, more generally, for an unsaturated soil in which the pores are filled by two fluids, air and water: The porosity
Hydraulic conductivity (K) is a property of soil that describes the ease with which water can move through pore spaces.
The water enters the soil through the pores by the forces of gravity and capillary action.
The largest cracks and pores offer a great reservoir for the initial flush of water.
The various pore size categories have different characteristics and contribute different attributes to soils depending on the number and frequency of each type.
Unless impeded, water will drain from these pores, and they are generally air-filled at field capacity.
Macropores can be caused by cracking, division of peds and aggregates, as well as plant roots, and zoological exploration.
The properties of mesopores are highly studied by soil scientists because of their impact on agriculture and irrigation.
Hand tracing and measurement of crack patterns on paper was one method used prior to advances in modern technology.
By measuring at the hydraulic conductivity at a range of negative potentials, the pore size distribution can be determined.
Horgan and Young (2000) produced a computer model to create a two-dimensional prediction of surface crack formation.
Depth, continuity, surface area and a number of other measurements can then be made on the cracks within the soil.
A specially designed resistivity meter had improved the meter-soil contact and therefore the area of the reading.