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Soil is essential to most animals on the earth. It is a relatively thin crust where an even smaller portion contains much of the biological activity. Soil consists of three different phases. A solid phase (≈ 50%) that contains mainly minerals of varying sizes as well as organic compounds. The rest is pore space. This space contains the liquid and gas phases. 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. ==Bulk density== (詳細は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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Characterisation of pore space in soil」の詳細全文を読む スポンサード リンク
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