How to obtain the saturation point of a soil layer from the volumetric soil water content data?

Question

Would you please let me know if the following is accurate as an answer to the question:
Suppose we have sensors which measure the volumetric soil water content of a soil layer for a long period (more than 6 months). Could I attribute the maximum (percentage) in this dataset to the saturation point?
I understand that we do need to have a lengthy rainfall event to have a saturated soil condition. How long the event should be so that the above proposal works?
And if there is any other way that I can get to the saturation point of a soil layer from the volumetric soil water content data/sensors, please let me know.
Mostly focused on the topsoil and preferably only using the dataset.
Thank you all.

haresfur · Accepted Answer

I assume you mean sensors that measure volumetric soil water content. The answer will depend on the amount of precipitation and the permeability of the soil. Soils don't reach full saturation in some climates - especially coarse texture soils. I would say that if the soil water content reaches a maximum value that persists for a period of time after large rainfalls (giving a flat top) and ideally reaches the same maximum level during multiple wetting-drying cycles that it is reasonable to infer that is the saturation value.
Ideally you would collect undisturbed soil samples of known volume (e.g in by driving a cylinder into the soil (gently as possible) to determine the pore volume and saturated water content.
Also be aware that many soil moisture sensors give readings that are dependent on soil properties and are not linear up to 100% saturation so they may not give good values at high water contents. It is best to calibrate those types on your soils.

How to obtain the saturation point of a soil layer from the volumetric soil water content data?

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