Information on visual or arithmetic required to be used would be great - or a peer review article reference. Thanks
You have to determine soil moisture with different depth with in the effective root zone, since soil bulk densities varied with the depth . Calculate the required water for bringing the given depth back to field capacity and the sum the required of all depths. Thanks
Update: I have hourly in-situ data for each depth. Also, sensors span effective root zone. The question is can I determine field capacity, not how to use it.
Time series data of soil moisture at four different depths do not enable to derive field capacity (Fc). There are two methods for this : (1) in situ measurement and (2) pedotransfer equations using soils textural composition
Kirk,
You can indeed estimate field capacity from soil moisture data, as long at ET is small (beginning of growing season). See the link below for details and examples.
https://www.decagon.com/en/support/datatrac-3-troubleshooting/how-do-i-determine-field-capacity/#Determining_Field_Capacity_and_Permanent_Wilting_Point
"You can also determine your field capacity value in the field using Decagon soil moisture sensors. The methodology below is a rough adaptation from Methods of Soil Analysis, Vol. 4 Methodology (Dane and Topp, 2002).
These tests are best done before the growing season as one of the assumptions of this estimate is that water is only being removed from the soil profile through drainage due to gravity
In a representative part of your field, before the growing season begins, install Decagon soil moisture sensors at the soil depths where you are interested in determining plant available water. We recommend at least three depths that cover the early and mid growing root zone as well as below the root zone.
Monitor the soil moisture immediately after an irrigation event or a rain event. After three days, in most soils, the water content levels will have stopped changing significantly suggesting that the remaining water content (assuming no evaporation or transpiration) is considered to be field capacity. In some finer textured soils, it may be necessary to wait 4-10 days for the water content to stop changing significantly."
In one of answers absolutely right definition of FC in the field of irrigating of the soil and after 3 days measurements of moisture on layers of soil. Of course it in case of automorphic conditions is described. There is more difficult in laboratory by method of definition of OVH or curve water-retaining ability. But if you know texture, it is possible to use the table.
http://www.terragis.bees.unsw.edu.au/terraGIS_soil/sp_water-soil_moisture_classification.html
Galina Stulina
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