Difference between soil water content and water holding capacity (WHC) from a soil ecological point of view.
Soil water content, we usually refer to either moisture retention between wilting point and field capacity or between any other two soil moisture constants. But water holding capacity is worked beyond field capacity . How much a soil can hold moisture without loss of moisture due to gravitational pull, for example moisture holding capacity at soil saturation...
Soil water content, we usually refer to either moisture retention between wilting point and field capacity or between any other two soil moisture constants. But water holding capacity is worked beyond field capacity . How much a soil can hold moisture without loss of moisture due to gravitational pull, for example moisture holding capacity at soil saturation...
Water Holding Capacity (WHC) is the maximum value of soil water content. It is could be present as v/v (percent of volume) either w/w (percent of weight).
Soil water holding capacity is the soil moisture content that will remain in soil after water drained off the large pores. Generally it is assumed that pores >50 µm diameter are not able to hold water against the force of gravity, which corresponds to a suction force of 60 hPa, or pF=1.8.
Soil water content is simply the amount of water stored in the soil regardless of its energy state. All states of water in the soil starting from hydroscopic moisture to state of saturation are soil water content, only differ in amount. Soil water holding capacity is, however, the ability of a soil to retain water. For instance, clay soils contains high water holding capacity than sandy soils.
Soil water content is the amount of water in the soil (plant available plus plant unavailable). It is measured by drying the soil sample at 105 degree Celsius to a constant weight (about 24 hours).
Water Holding Capacity of a soil is the maximum amount of water a soil can hold for crop use. Since in theory, agronomic crops can use the water between Field Capacity and Permanent Wilting Point (-15 bar), thus by measuring these 2 points, and taking the difference, water holding capacity of the soil can be calculated. Since soil moisture at FC and PWP are affected by soil texture and soil structure, thus water holding capacity is also affected by soil texture and structure.
From ecological point of view, some plants are drought tolerant, which we are called Xerophytes. Xerophytes can tolerate drought and their PWP are usually even less than -15 bar (some of them can tolerate PWP of -20 bar or more). Thus, WHC of soil in natural systems or ecosystems that are dominated with Xerophytes, are higher than WHC of agronomic soils.
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The water content of the soil is either the mass of water divided by the mass of dry soil particles (gravimetric water content) or the volume of water divided by the volume of the soil (volumetric water content). The relationship to convert from gravimetric (W) to volumetric (T) is T = Wxrb/wb, where rb is the bulk density of the soil and wb is density of water. The density of water is 1 g/cm3 or 1000 kg/m3, so is often not included in the formula. Note water content is unit less.
The water holding capacity of soil is the mass or volume of water between two values. These values are usually the field capacity water content as the upper limit and water at a lower limit. The available water capacity (AWC) uses a lower limit of the wilting point (often taken as the water content at a matric potential of -15 bar) and the plant available water capacity (PAWC) is the water that plants can easily extract. The PAWC is often measured in the field and various authors have used different values of the matric potential (often -1 bar). This is because the lower limit for PAWC will vary with the evaporative demand.
You will find a lot of information on this in the literature. Try using google scholar.
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