If the water retention curve is available for a given soil, we can calculate soil moisture based on the value of soil water matrix potential. And then we can compute the water filled pore space from the soil bulk density.

Water tension table could be performed for fresh undisturbed soil, or air-dried soil.

Best wishes.

Hello Xin Shu! By water retention curve calculated differential porosity of soils (distribution of pore size) coefficients of water conductivity and filtration of soils. Based on these data, calculate the irrigation rate and irrigation time of soils.

Hello Xin Shu, the relationship between the water retained in the pore space and the matric potential (pF) is irregular. If consider the volumetric water content (Vwc) at the bottom pF ( 0.6, although the pF increases are strong, changes in Vwc remain very low. Of course this development also depends on the soil texture. Best regards.

Dear Dr. Xin Shu,

If you have information about the water retention curve for the soil that you are working, you can obtain through values of water matric potential the amount of water by volume using the concept of the volumetric soil water content (water by volume/volume of soil).

If you are working with samples collected in volumetric rings, you have information about the volume of your soil. So, as I said, having the soil water content for a specific value of matric potential, you can easily evaluate the water by volume for your sample. If you previously determined the total porosity of your soil, you can measure the WFPS for that specific matric potential.

If you differentiate your water retention curve you can obtain the pore size distribution curve, and has the possibility of relate the variations in WFPS with the distribution of pores.

Regards.

Hi

Soil water retention curve is the relationship between soil matrix potential and soil moisture content (by weight or by volume); of which i prefer soil volumetric water content. So by obtaining this curve and measuring soil matric potential by tensiometer, you will get an idea of how much water you have in soil and if there is a need to irrigate or not, and how much to irrigate.

As Dr. Moiseev mentioned above, this curve can be used to calculate differential porosity. So by using this curve and appropriate techniques, you may calculate the pore size distribution of the pores that can retain water.

If you want to start measuring your water retention curve from saturation point, then you do not need to oven dry it. you may use the fresh sample and saturate it first and start your pressure plate procedure.

good luck

Thank you for suggestions and view points. They are quiet useful.

Now I am using tension table to get the retention curve, however, each time when I change the pressure, there always air come into the system. How can I get rid of the air? Much appreciate.

Xin

Dear all,

Have you used the tension table to do soil retention curve? Why the soil is cracked during the experiment? I can see a fissure at the surface. What should I do to solve the problem? Should I keep going by using this cracked soil or make a new one?

Many thanks.

Xin

Dear Xin Shu,

First, it is necessary to check the composition of your soil. If you are working with expansive clay (2:1 clays) - it is possible to confirm the soil mineralogy by using DRX analysis - will be hard to you control the fissures inside your samples. I think that obtain a new sample will not solve your problems. However, if the soil presents this behavior in the field, I suggest to you to continue using these samples with fissures. However, it is also necessary to verify the existence of changes in the sample volume to evaluate if the tension table is the best method.

Regards,

Luiz