Frequently Asked Questions
- Water potential - Soil moisture release curves - WP4C - HYPROP - LABROS We have a HYPROP and WP4C. What challenges can we expect with analyzing high-clay vertisol soils?
This is a really good question. One of the main issues you will see with the high clay vertisols will be the shrinking of the samples during the measurements. You shouldn’t have too much of an issue with contact during the measurement. Due to the volume change during the measurement, the VWC measured by the HYPROP won’t correlate well with the actual change in volume. The VWC and bulk density will be based on the saturated volume and density of the soil samples. One way to approach this is to convert to gravimetric water contents.
- Hydraulic conductivity - HYPROP - GENERAL Is hydraulic conductivity at near saturation unreliable for higher suctions?
It’s not that unsaturated hydraulic conductivity near saturation is unreliable but that some measurement methods have difficulty making that measurement, for example: the flow cell vs. the HYPROP. The HYPROP has issues near saturation because there is not enough difference between its two tensiometers. The flow cell approach does a better job of measuring unsaturated hydraulic conductivity near saturation. So it just depends on the method you use.
- Hydraulic conductivity - HYPROP - GENERAL If field and lab measurements are different, is it recommended to complete the hydraulic conductivity curve obtained with HYPROP in the lab with field measurements in the HYPROP-Fit?
This will depend on your research goal. If your goal is to understand individual types of soil (i.e., what are the intrinsic soil properties of a B horizon) then a better approach is to take lab measurements because you have better control. But if your goal is to understand interactions in the field, a better approach is to make field measurements.
- Hydraulic conductivity - HYPROP - GENERAL - KSAT - MINI DISK INFILTROMETER Can you refer me to a reliable measurement method to estimate and predict unsaturated hydraulic conductivity?
- Hydraulic conductivity - SATURO - HYPROP - GENERAL How could one determine the change in hydraulic conductivity at a soil-spoil interface?
There are two approaches you could take. You could measure the two materials independently and see which one is going to be most limiting. Typically, hydraulic conductivity is governed by the most limiting layer. You could also just make the measurement in the field and see the interaction between the two layers. Again this rate will be governed by the most limiting layer.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - LABROS Does field capacity vary depending on whether the soil has previously been in a dry or wet state? If so, what error margin might that cause if I plan irrigation scheduling according to FC?
This is true. What you are looking at is the effect of hysteresis, which is generally not a big concern. Depending on the soil type and how big the hysteresis effect is, it can actually shift the field capacity point slightly. If you are concerned about this, you may want to use water potential to schedule irrigation, for example with the TEROS 21 or a tensiometer. If you’d like more information about this, contact customer support.
- TEROS 21 - Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - T8 Tensiometer - T4 Tensiometer - T5 Tensiometer - LABROS How can you measure capillary water potential?
Capillary water potential is tied to matric potential. So if you are measuring matric potential with a tensiometer or a TEROS 21, you are essentially measuring the effect of the capillaries or those different pore sizes. You can also use the HYPROP. The WP4C will also work assuming the soil has a negligible osmotic potential.
- TEROS 21 - Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - T8 Tensiometer - T4 Tensiometer - TEROS - T5 Tensiometer Do matric potential sensor readings include osmotic potential?
This depends on what type of instrument you are using to measure the potential. For example, tensiometers, granular matric sensors, and the TEROS 21 ONLY measure matric potential. So these sensors are blind to osmotic potential. Laboratory instruments like the WP4C measure both osmotic and matric potential. But in terms of field sensors, there aren’t any that give both components.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - LABROS We monitor soil moisture using water content. How can we integrate this into a soil moisture release curve?
One of the best ways to do this is to take some samples and measure the soil moisture release curve for that soil, generating a functional relationship. Then you can take that curve and use your water content values to set your irrigation points through your release curve function. Another option is modeling it. If you know some information about the soil type and pedology, there are pedotransfer functions you can use by inputting those variables, and it will predict a soil moisture release curve. This method is not as accurate, but it’s a possible option.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL Which depths should I consider for active roots in maize for irrigation management?
You can refer to the literature for rooting depths of maize. As for the sensors, we recommend a combination of TEROS 12 soil moisture sensors and TEROS 21 matric potential sensors to get the whole picture.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - LABROS What modeling programs can you use to model soil moisture release curves?
There are a few different models out there to model soil moisture release curves. ROSETTA is a program from the US Salinity lab that has been around for a long time. Hydrus is another tool that can be used to model soil moisture release curves. One thing to remember is that these models don’t take into account all of the factors that can change a soil moisture release curve. So if you decide to model your soil moisture release curve, remember they aren’t perfect.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - LABROS Now VWC trends are used to determine field capacity and stress onset. Is this a more accurate method than water potential?
This is one approach to take. The issue with using water content measurements is you have to wait until you observe stress occurring to make this type of set point. We recommend a physical water potential measurement as a better way to determine a stress set point. As for field capacity, you can still use the physical measurements to set your field capacity point. The most important thing to understand is that the traditional -33 kPa point for field capacity is not a good rule of thumb to follow. Read why here.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - LABROS How do you develop a soil moisture release curve in highly variable soils?
If you have a site with highly variable soils you will need to generate a curve for each individual soil type. One approach would be to map out the site and select the soil types of most importance and then create soil moisture release curves for those soils.
- Water potential - Soil moisture release curves - WP4C - HYPROP - Volumetric Water Content - GENERAL - LABROS Do private chemical labs carry out soil water retention curve analysis? Or just university labs?
There aren’t many private labs that offer retention curve services, however, METER does offer soil moisture release curve services. Find it here.
- TEROS 21 - Water potential - Soil Moisture Sensor - WP4C - HYPROP - GENERAL What is matric potential?
Matric potential is the force that would need to be exerted to move a water molecule from the surface of a soil particle. For example, a matric potential of -100 kPa would require a force of -101 kPa to pull that water molecule off of the soil particle. It is one component of the total water potential. Learn more about the different components of water potential here.
- HYPROP - LABROS How do I connect more than one HYPROP sensor to HYPROP View? Connect only one HYPROP sensor at a time to check the Device ID number when you purchase a new sensor. Each HYPROP should have a unique Device ID. Change the Device ID if it is the same number as your other HYPROP sensor. To do this, select “Show Devices”. Right click the sensor, and click Change Device ID.(Note: Older HYPROP software may not be compatible with newer sensor units. If needed, upgrade the HYPROP View software).Use the Help Wizard to see each step with pictures (or view this video).
- HYPROP - LABROS Why does the scale not record the weight during the measurement?
There are two possibilities:
- The scale was not switched on. The scale will be detected by the software but cannot log any data. When the scale is switched on, the weight appears in its display.
- The scale is being used in a wrong mode and therefore cannot log the weight. In Single Balance Mode, there is no automatic measurement of the weight. The weight changes need to be taken one by one and recorded by the software. In Multi Balance Mode, the weight changes will be recorded automatically. Review the section “Measuring” in the user manual for more information.
- The default settings on the scales were changed. Check to ensure that the scale settings match the defined settings shown in the user manual (section “Preparing a Measurement” under “Default Settings”).
- HYPROP - LABROS How do I complete a HYPROP measurement?
You can finish a measurement in three ways:
- You can stop when the top tensiometer shaft has reached the cavitation phase (see illustration 1). Then you will not use the air entry point.
- If you are willing to use the air entry point. Then there are two possibilities:
- The air entry point of the top tensiometer shaft has been reached and the bottom tensiometer shaft is still in the regular measurement range (phase 1) or in boiling delay (phase 2). In this case, the HYPROP can calculate the median value of the top tensiometer and bottom tensiometer curve (see illustration 2).
- When the air entry point of the top tensiometer shaft has been reached and the bottom tensiometer shaft is still in the cavitation phase (phase 3), the median value of the two cannot yet be calculated. If this is the case, wait until the air entry point of the bottom tensiometer shaft has been reached (see illustration 3).
- HYPROP - LABROS What four phases should I see if the tensiometer shafts and sensor unit are properly degassed?
Phase 1: Regular measurement range
In phase 1, the tension value increases without flattening until it reaches the boiling point of water.
Phase 2: Boiling delay phase
In phase 2, the tension value increases to the boiling delay area (above ambient air pressure). This is nice to have, but in general not necessary for the evaluation.
Phase 3: Cavitation phase
In phase 3, water vapor is generated in the tensiometer shaft, and then the tension value drops abruptly down to the boiling point. After this, the tension value decreases only slightly.
Phase 4: Air entry phase
In phase 4, the tension value drops abruptly to zero as air penetrates the ceramic. The air entry point is a material characteristic of the ceramic and amounts to about 8800 hPa (880 kPa). This point can also be used for the evaluation.
- HYPROP - LABROS Why does my HYPROP read 4000 hPa (400 kPa)?
The pressure sensor may be damaged, so the sensor unit should be checked. Contact METER Group support or your local dealer. The sensor unit will likely need to be sent in for repairs.
- HYPROP - LABROS What should I do if the software does not find any sensor units in the Single Balance Mode?
Disconnect the sensor units one by one and have the software show the device tree. Check the device tree to see if one or more sensor units have the same address. Review the section “Preparing a Measurement” in the user manual for information about changing the sensor unit address.
- HYPROP - LABROS What can cause the bottom tensiometer to “overtake” the top tensiometer?
The tensiometer shafts may have been switched around. There is no need to interrupt the measurement since you can correct this in HYPROP-FIT.
- HYPROP - LABROS What do I need to check if data stops recording in the middle of a measurement?
Check the cable connection to the USB port. Change the energy management of your computer to Continuous Operation (which is typical when using a laptop). If using a USB hub, make sure it is properly powered.
- HYPROP - LABROS What if the tension value exceeds atmospheric pressure (e.g., 1000 hPa or 100 kPa)?
This is not a problem, and it is a result of proper degassing and causing a boiling delay. This means you can extend beyond the “normal” measuring range of the HYPROP.
- HYPROP - LABROS What can cause the tension value to reach 500 – 700 hPa (50 – 70 kPa) and then drop?
This can happen if water in the tensiometer shaft was not degassed well enough. Check the degassing process to ensure you are reaching full vacuum (above 85 kPa depending on your elevation). This can also happen if the red O-ring that seals the tensiometer shaft is not sealing properly. Check for damage, and if necessary, replace the O-ring (review “Cleaning and Maintenance” in the user manual).
- HYPROP - LABROS What steps should I take to remove bubbles from the tensiometer shaft?
Repeat the refilling step for tensiometers, and use degassed water. If bubbles remain in the shaft, check for leakage around the shaft, and fix the leak if one is found. You may need to replace the red O-ring of the tensiometer shaft.
- HYPROP - LABROS How can I combine my WP4C data with data from my HYPROP®?