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The disc permeameter is a field instrument used for measuring water infiltration in the soil, which is characterized by in situ saturated and unsaturated soil hydraulic properties. It is mainly used to provide estimates of the hydraulic conductivity of the soil near saturation. ==History== Conventional techniques for measuring in-situ infiltration include the use of a single or double ring infiltrometer. Single and double ring infiltrometer only measures flow under ponded (saturated) conditions, and when used in soil with distinct macropores, preferential flow will dominate the flow. (See: Poiseuille's law) This does not reflect infiltration under rainfall or sprinkler irrigation. Therefore many authors attempted to create a negative potential (tension) on the water flow. This is to exclude macropores in the flow process, hence only measuring the soil matrix flow. Willard Gardner and Walter Gardner developed a negative head permeameter as early as 1939. Dixon (1975) developed a closed-top ring infiltrometer to quantify macropores. Water is applied to a closed-top system, which permits the imposition of negative head or pressure on the ponded water surface. Negative tension can be considered as simulating a positive soil air pressure, created by a negative air pressure above ponded surface water. A simplification was made by Topp and Zebchuk (1985). The limitation of this device is the infiltration has to be started by ponding the closed-top infiltrometer (applying a positive head), then adjusted to a negative pressure. Little research effort was continued in this area, instead attention has been given mainly to the sorptivity apparatus of Dirksen (1975) which used a ceramic plate as a base. Based on this design, Brent Clothier and Ian White (1981) developed the ''sorptivity tube'' which can provide a constant negative potential (tension) on the soil surface. However, the ''sorptivity tube'' had many shortcomings, hence modifications to the design led to the development of the ''disc permeameter'' by Perroux and White (1988) from CSIRO. In the US it is known as the ''tension infiltrometer''. For more on the development of the first permeameter as told by Walter Gardner, visit (http://www.decagon.com/ag_research/hydro/history.php) 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「Disc permeameter」の詳細全文を読む スポンサード リンク
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