Can total porosity be deduced from the water holding at saturation? That is when soil is at saturation does that mean all pore spaces are filled with water? If this is true can one assume that the total water at saturation is equal to total porosity?
Total porosity is the percent of the soil volume occupied by pore spaces, water- holding capacity is the percent of the soil volume that contains water, and air-filled porosity is the percent of the soil volume that is filled with air
Saturation is the point whereby a soil has reached it's maximum water holding capacity while Porosity is the volume of pore spaces present in a soil.
The pore spaces are filled with air and water, hence, the answer is no.
To get the total porosity of a soil, you have to add the air filled volume and water filled volume of the soil.
Saturation is the point whereby a soil has reached it's maximum water holding capacity while Porosity is the volume of pore spaces present in a soil.
The pore spaces are filled with air and water, hence, the answer is no.
To get the total porosity of a soil, you have to add the air filled volume and water filled volume of the soil.
If all of the total pores of soil are filled with water then the soil is fully saturated (the soil moisture content at this point is called theta s). Theta s is the total water that can retain in soil and is the sum of the capillary water and non-capillary water. Ideally, theta s should be equal to the porosity of the soil. This happens in a laboratory condition when one saturates the soil in controlled conditions such as a vacuum. However, in natural conditions, not all of the soil pores are filled with water and usually, some air will be trapped in soil pores (entrapped air). The entrapped air should be around 5 percentage -or less- of the total porosity of the soil!
Total porosity is the percentage of the volume of pore space of a soil filled up with air and water. Alternatively, a soil has reached maximum water holding capacity at its saturation point. However, these two things/terms are not the same.
By its definition, yes. But it's the same or below. Many factors are involved with the process.
Dear Portia Phohlo, No, they are not the same since, at saturation, there could still be pores in the soil that contain air in the form of bubbles. However, the actual difference in values between total porosity (TP) and total water holding capacity at saturation (WHCs) of soil could be very small. This is the reason why some books on soil analysis use the value of WHCs as an estimate of TP.
Nice discussion already taken place . I am bit late in joining the discussion . Very good question tossed up by Portia.
Soil porosity refers to the space between soil particles, which consists of various amounts of water and air. Porosity depends on both soil texture and structure. For example, a fine soil has smaller but more numerous pores than a coarse soil. A coarse soil has bigger particles than a fine soil, but it has less porosity, or overall pore space. Water can be held tighter in small pores than in large ones, so fine soils can hold more water than coarse soils.
Soils with smaller particles (silt and clay) have a larger surface area than those with larger sand particles, and a large surface area allows a soil to hold more water. In other words, a soil with a high percentage of silt and clay particles, which describes fine soil, has a higher water-holding capacity.
Source: Enclosed as below
Hello Portia,
greetngs from Osnabrueck ...
Is the total water content (at saturation) equal to the total porosity of a soil sample?
But only if all pore spaces are filled with water.
That is when soil is at saturation does that mean all pore spaces are filled with water?
Yes, in the LABORATORY soak the undisturbed soil sample in the sampling ring in a water bath without destroying the soil structure.
Can total porosity be deduced from the water holding at saturation?
Yes, with a limitation. However, the difference in weight between the totally soaked soil sample and the soil sample dried in the drying oven.
Soak the undisturbed soil sample in a water bath in the laboratory. Weigh the totally watered soil sample without drip loss. Then dry the watered soil sample at 105°C in the drying oven. The dried soil sample is weighed again. The difference in weight between the totally watered soil sample and the dry soil sample is the total pore volume of the soil.
This weight difference is to be calculated by volume% total pore volume.
However, this method is very unusual.
Total pore volume = coarse pores + medium pore + fine pore
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