The quick summary of that tl;dr page is that there are two separate concepts:
Volumetric Water Content (VWC), which is the fraction of any volume of soil that is water. This is dimensionless, and typically in %. Water potential, reported as pressure The wilting level of a plant depends on water potential, and the relationship between VWC and water potential is highly dependent on soil type. Field capacity is the moisture after soaking and draining (but not evaporation or plant use, I think). With my WH51, it seems reasonably clear that it's trying to measure VMC, and my experimentally determined 22%/40% makes sense. The Davis sensor is very clearly water potential with a negative sign, termed "suction" and in pressure units. The spec sheet says: https://www.davisinstruments.com/product_documents/weather/spec_sheets/6440_SS.pdf https://irrometer.com/sensors.html The Soil Moisture/Temperature Station converts the electrical resistance reading from the sensor into a calibrated reading of centibars of soil water suction with a range from 0 (wettest) to 200 (driest) centibars. The metergroup page gives an example of -0.3 Mpa, or -300 000 Pa. Midrange in Davis is 100 cb which is 1 bar, and mulitplying by 100 000 Pa/bar gets -100 000 Pa. This doesn't quite line up as the example is 1.5x the top range, but it could be that typical soil for a non-irrigated tree is much drier than for crops. Architecturally, weewx should have separate column names with associated units for VWC and either suction or water potential, deciding on positive/negative. That's my theory right now and I'm sticking to it for at least an hour! -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to weewx-user+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/rmih7ocppgu.fsf%40s1.lexort.com.
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