Water retention curve

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, 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.

Mualem–van Genuchten shape parameters

The shape of water retention curves can be characterized by several models, one of them known as the Mualem–van Genuchten model [cite journal |author=Mualem, Y. |year=1976 |title=A new model for predicting the hydraulic conductivity of unsaturated porous media |journal=Water Resources Research |volume=12 |pages=513–522 |doi=10.1029/WR012i003p00513 ] [cite journal |author=van Genuchten, M.Th. |title=A closed-form equation for predicting the hydraulic conductivity of unsaturated soils |journal=Soil Science Society of America Journal |year=1980 |volume=44 |issue=5 |pages=892–898 |url=http://hydro.nevada.edu/courses/gey719/vg.pdf ] :: heta(psi) = heta_r + frac{ heta_s - heta_r}{left [ 1+(alpha |psi|)^n ight] ^{1-1/nwhere: heta(phi) is the water retention curve [L3L−3] ;:|psi| is suction pressure ( [L−1] or cm of water);: heta_s saturated water content [L3L−3] ;: heta_r residual water content [L3L−3] ;:alpha is related to the inverse of the air entry suction, alpha >0 ( [L−1] , or cm−1); and,:n is a measure of the pore-size distribution, n>1 (dimensionless).


In 1907, Edgar Buckingham created the first water retention curve [cite journal |last=Buckingham |first=E. |title=Water retention in soil |journal=Soil Bulletin |issue=38 | publisher = U.S. Department of Agriculture |year=1907 ] . It was measured and made for six soils varying in texture from sand to clay. The data came from experiments made on soil columns 48 inch tall, where a constant water level maintained about 2 inches above the bottom through periodic addition of water from a side tube. The upper ends were closed to prevent evaporation.


*cite book |last=Brady |first=N.C. |title=The Nature and Properties of Soils |edition=12th Edition |publisher=Prentice-Hall |year=1999 |location=Upper Saddle River, NJ |pages=pp. 183-9 |isbn=0138524440

Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Water retention — can refer to: *Edema or peripheral edema *Premenstrual water retention *A water retention curve for soil water potential …   Wikipedia

  • Water content — Soil composition by phase: s soil (dry), v void (pores filled with water or air), w water, a air. V is volume, M is mass. Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture),… …   Wikipedia

  • Runoff curve number — The runoff curve number (also called a curve number or simply CN) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess.[1] The curve number method was developed by the USDA Natural… …   Wikipedia

  • Pedotransfer function — (PTF) is a term used in soil science literature, which can be defined as predictive functions of certain soil properties from other more available, easily, routinely, or cheaply measured properties. This concept arises in soil science as… …   Wikipedia

  • Integral energy — is the amount of energy required to remove water from an initial water content heta i to water content of heta f (where heta i > heta f). It is calculated by integrating the water retention curve, soil water potential psi( heta) with respect to… …   Wikipedia

  • Hysteresis — Not to be confused with Hysteria. Fig. 1. Electric displacement field D of a ferroelectric material as the electric field E is first decreased, then increased. The curves form a hysteresis loop. Hysteresis is the dependence of a system not… …   Wikipedia

  • Fractal in soil mechanics — The fractal approach to soil mechanics is a new line of thought. There are several problems in soil mechanics which can be dealt with by applying a fractal approach. One of these problems is the determination of soil water characteristic curve… …   Wikipedia

  • Vadose zone — [ capillary fringe, water table, and phreatic or saturated zone. (Source: United States Geological Survey.) ] The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic zone or zone of… …   Wikipedia

  • Tensiometer — A tensiometer is a device used to determine matric water potential Psi m (soil moisture tension) in the vadose zone. The tensiometer consists of a glass or plastic tube with a porous ceramic cup, and is filled with water. The top of the tube has… …   Wikipedia

  • WRC — Die Abkürzung WRC steht für: die World Rally Championship, siehe Rallye Weltmeisterschaft das gleichnamige PlayStation 2 Spiel, siehe World Rally Championship (Computerspiel) World Rally Car, ein Rallyeauto der Top Kategorie die World… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”