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I would like to use the layer for Field Capacity, Wilting Point & Available Water Content (difference between field capacity & wilting point). What does the following attribute mean as mentioned in the metadata file of SoilGrids v1 -

  1. Derived available soil water capacity (volumetric fraction) with FC = pF 2.0 for depth 0 cm
  2. Derived available soil water capacity (volumetric fraction) with FC = pF 2.3 for depth 0 cm
  3. Derived available soil water capacity (volumetric fraction) with FC = pF 2.5 for depth 0 cm
  4. Derived available soil water capacity (volumetric fraction) until wilting point for depth 0 cm
  5. Derived saturated water content (volumetric fraction) teta-S for depth 0 cm
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These attributes are Field capacity at different tensions:

pF 2.0 corresponds to KPa = 10

pF 2.3 corresponds to KPa = 20

pF 2.5 corresponds to KPa = 33

Depth 0 is the first depth layer predicted.

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  • Thank you for the response @Jorge ! I wanted to calculate Available Water Content based on the difference in Field Capacity and Wilting Point for a location. So, what are your suggestions for layer selection, if Field Capacity and Wilting Point for a location are to be identified. Additionally, what do the following parameters mean as mentioned in the 4th and 5th bullet point in the original question. – Vaibhav Chhipa Nov 11 '20 at 11:46
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I was using SoilGrids data as well to calculate these values. I took a different approach. I used the sand, clay, and organic matter content at different levels, along with a paper that I found by Teh, C.B.S called "Development and Validation of an Unsaturated Soil Water Flow Model for Oil Palm".

https://www.researchgate.net/publication/321905343_Modeling_soil_water_flow_in_Python_and_Excel

In it it gives equations to use sand, clay, and organic matter content (as a %) to derive the:

  • permanent wilting point (theta_1500)
  • field capacity (theta_33)
  • and, saturation (theta_0) For the various levels.

They refer to the Saxton Rawls equations from 2006 which is some sort of curve fit. The equations are long so I'm not going to put them here. If you cannot find them in the paper let me know.

Using SoilsGrid data I had to derive organic matter content as:

OM = (Organic Carbon Density in g/dm3) / { 100 * (Bulk Density in cg/cm3) }

both terms on the right are values supplied by SoilGrids. I have a question out to them to confirm I'm deriving this correctly. Sand and Clay content values I used as is from SoilGrids (divided by 1000 to get %).

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