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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Water retention curve ： ウィキペディア英語版 Water retention curve Water retention curve is the relationship between the water content, θ, and the soil water potential, ψ. This curve is characteristic for different types of soil, and is also called the soil moisture characteristic. It is used to predict the soil water storage, water supply to the plants (field capacity) and soil aggregate stability. Due to the hysteretic effect of water filling and draining the pores, different wetting and drying curves may be distinguished. The general features of a water retention curve can be seen in the figure, in which the volume water content, θ, is plotted against the matric potential, $\backslash Psi\_m$. At potentials close to zero, a soil is close to saturation, and water is held in the soil primarily by capillary forces. As θ decreases, binding of the water becomes stronger, and at small potentials (more negative, approaching wilting point) water is strongly bound in the smallest of pores, at contact points between grains and as films bound by adsorptive forces around particles. Sandy soils will involve mainly capillary binding, and will therefore release most of the water at higher potentials, while clayey soils, with adhesive and osmotic binding, will release water at lower (more negative) potentials. At any given potential, peaty soils will usually display much higher moisture contents than clayey soils, which would be expected to hold more water than sandy soils. The water holding capacity of any soil is due to the porosity and the nature of the bonding in the soil. ==Shape parameters== The shape of water retention curves can be characterized by several models, one of them known as the van Genuchten model: :$\backslash theta(\backslash psi)\; =\; \backslash theta\_r\; +\; \backslash frac\{\backslash left(1+(\backslash alpha\; |\backslash psi|)^n\; \backslash right)^\{1-1/n\}\}$ where :$\backslash theta(\backslash psi)$ is the water retention curve (); :$|\backslash psi|$ is suction pressure (() or cm of water); :$\backslash theta\_s$ saturated water content (); :$\backslash theta\_r$ residual water content (); :$\backslash alpha$ is related to the inverse of the air entry suction, $\backslash alpha\; >0$ ((), or cm−1); and, :$n$ is a measure of the pore-size distribution, $n>1$ (dimensionless). Based on this parametrization a prediction model for the shape of the unsaturated hydraulic conductivity - saturation - pressure relationship was developed. 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「Water retention curve」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.