Is there any method to deal such as. Problem is, I have estimated the soil water/moisture contents at two depths e.g 20cm and 40cm now I want to estimate the soil water/moisture values in between these two depths (like 25/30/35cm or any) and don't want to install new sensors for every depth.
Assuming there are no changes in soil texture or structure, a simple proportional approach wold give you the soil moisture (theta) content at each soil depth. For example; Theta20cm = 0.40 Thta40 cm=0.30; then the theta rate of change is= (40-30)/20=0.05 cm/cm per cm of soil. Theta21cm=0.395; theta25cm=0.375; theta30cm = 0.35. An so on.
Assuming there are changes in soil texture and soil structural parameters WEIGHT by changes in soil water pressure.
Hope these comments help you to evaluate soil moisture content for any soil depth in your soil profile.
Kind Regards
Sincerely
Jose Navar, Ph.D OSU
Estimation of soil moisture at different depth is generally done on the basis of gravimetric method in which the sample is drawn like 0-20 cm and 20-40 cm mean the sample is representing the 0-20 cm soil and 20-40 cm soil depth. As the crop root zone is distributed in soil, layerwise soil moisture content will be more useful for planning of irrigation. Mean you need to develop a sensing prob rather than a point
If you have two sampling points of humidity at 20 and 40 cm, I do not see the need to measure humidity at 30 cm because, as Dr. Navar says, without changes in the structure and texture of the soil, it will be proportional To both measures. It will also depend on whether the soil is dampening or drying.
The question is very important, as everyone tries to predict the soil moisture in the sub-soil (deeper layers) on the basis of surface soil moisture, which can subsequently be used in operational application of remote sensing, where we can estimate the surface moisture through sensors and thereafter predict the overall profile moisture. In this process, we have to use the moisture retention, release and transmission characters alongwith the land use types on that soil. We need to develop transfer functions to estimate this.
Soil textural distribution with depth plays an important role in this regard, and historic season wise distribution of moisture over depths relationship can be drawn with the surface moisture content for the test field
regards
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