Frequently Asked Questions
- Soil Moisture Sensor - ECH2O 5TE - GS3 Can your 5TE or GS3 tell me the soil salinity or the pore water EC?
Our sensors measure bulk EC, not soil salinity or pore water EC. Pore water EC can be derived from bulk EC using various models, including the Hillhorst model. This is described more in our application note about soil EC.
- SC-1 Leaf Porometer - ATMOS Why doesn’t the Leaf Porometer output transpiration like the LI-COR used to?
The SC-1 Leaf Porometer measures the vapor flux to arrive at stomatal conductance, which on the surface gives you leaf level transpiration. However, the leaf chamber of the SC-1 forces its own environment on the leaf, so the chamber steady-state transpiration will likely differ significantly from the environment steady-state transpiration. This is fine for stomatal conductance since the reading is taken within 30 seconds, but it doesn’t work for transpiration. We recommend you use independent atmospheric vapor pressure and leaf temperature measurements coupled with an estimate of leaf boundary layer conductance to calculate transpiration from the stomatal conductance measurement made with the SC-1.
- ECH2O 5TE - ECH2O 5TM - Volumetric Water Content - GENERAL - ECH2O EC-5 - ECH2O Why don’t your soil moisture sensors measure with 1% accuracy like some others spec’d?
There are two elements to the accuracy of time-domain reflectometry (TDR), frequency domain reflectometry (FDR), and capacitance sensors:
- How well the sensors measure the dielectric permittivity of the soil; and
- How well the calibration converts that measurement to water content.
Due to inherent variability in soil physical properties, it is impossible for a dielectric sensor to measure within 1% water content accuracy across a broad range of soil types, even with a perfect measurement of dielectric permittivity. Beware sensors that claim an unbelievable accuracy in all substrates.
- KSAT - LABROS How does KSAT calculate the temperature correction to obtain the saturated conductivity at the specified reference temperature?
KSAT uses the temperature dependency of the viscosity of water to recalculate the reference conductivity (at your specified reference temperature) from the measured value (at the measured operation temperature). Details are specified on page 11 in the KSAT operation manual (available as a pdf from the Help menu in the KSAT software).
- WP4C - LABROS What causes long read times in my WP4C?
Contamination of the sample chamber is the primary cause of long read times. The WP4C relies on equilibration of water vapor in the chamber with the sample. A dirty sample chamber can have samples that adsorb or desorb water vapor. This can lead to longer read times but is usually rectified by a good cleaning.
Unstable temperatures can also be a problem. Take care to provide a stable temperature environment for your WP4C and to keep your samples close to the temperature at which you intend to read them.
- SATURO - HYDROS What is the maximum measurable infiltration rate of the DualHead Infiltrometer (SATURO)?
The SATURO can measure a maximum field saturated hydraulic conductivity (Kfs) of 115 cm/hr.
- Soil Moisture Sensor - GENERAL Why doesn’t my soil moisture sensor read 100% VWC in pure water?
Testing your sensor in water can be a great quick check for basic sensor function, but it is a poor test for accuracy. The calibration of all METER soil moisture sensors is optimized for 0 – 50% volumetric water content (VWC), the usual range of soil water content.
Water will tell you if a sensor responds to a change in water content. But the reading itself will vary. Please contact firstname.lastname@example.org for recommendations to test the absolute accuracy of your sensors.
- Soil Moisture Sensor - GENERAL What does my soil moisture value in a frozen soil mean?
Volumetric water content (VWC) from a frozen soil will look much like dry soil. Your sensor will carry on merrily, but you will not see any change in water content until you start to get liquid water near the sensor again.