Frequently Asked Questions
- 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 - GENERAL What is more significant to measure for irrigation: saturated or unsaturated hydraulic conductivity?
Saturated hydraulic conductivity is more significant in this application because it’s important to understand what will be the most limiting factor. As the soil is wetting up, there are matric forces that help pull water into the soil. But as we approach saturation near the surface, there may be ponding of water which could ultimately lead to runoff, and that will affect what your irrigation rates can be.
- 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 - GENERAL What is the difference between infiltration and unsaturated hydraulic conductivity?
Infiltration and hydraulic conductivity are related. Infiltration is a measure of a soil’s ability to infiltrate water from the surface, and it will change as the soil’s moisture conditions change. Infiltration rate is not typically corrected for three-dimensional flow and is not referenced to specific moisture condition. Hydraulic conductivity is a one-dimensional value that is specified to a specific moisture condition and can be used when trying to model water movement in soil. The equation that shows the relationship between infiltration and hydraulic conductivity is shown on slides 10 and11 of this webinar.
- Hydraulic conductivity - GENERAL Is it appropriate to measure hydraulic conductivity at plot level season after season?
Season-to-season variability will depend a lot on management. From a land management/treatment perspective, if there are things being done that will ultimately lead to improved soil structure and hydraulic properties, you may need to look at seasonal differences. If the land is always being managed the same, you may not see much of a difference in soil hydraulic properties season to season.
- Hydraulic conductivity - GENERAL What is the importance of hydraulic conductivity at plot level, for example, 5×5 plots with the same land use (e.g., a corn field)?
Hydraulic conductivity can be important, even at the plot level. It depends on the variability of the soils within the area. Even if the site is under the same land use, we can see variability in the soils across a small area which can result in a difference in hydraulic properties.
- Hydraulic conductivity - GENERAL What parameters are the most important to consider a soil as “healthy”?
There are many parameters to consider, and each is important. Typically, researchers look at parameters that relate to a more stable soil: improved aggregate stability, improved nutrient levels, and more biological activity. There are several groups working in this area, I would recommend looking at the work being done by the Soil Health Institute as starting point.
- Hydraulic conductivity - SATURO - GENERAL - MINI DISK INFILTROMETER How does soil structure affect K values? How are they related?
Soil structure and aggregate stability will have a large impact on the hydraulic conductivity values. Depending on the type of soil structure that is formed and the strength of that structure you will see a larger development of macropores within the soil which will have the ability to transmit more water than if the soil had poor structure or no structure. Learn more about this here.
- Hydraulic conductivity - SATURO - GENERAL - MINI DISK INFILTROMETER How would you measure horizontal hydraulic conductivity in field conditions? How would you disaggregate the horizontal component of hydraulic conductivity from the vertical one?
This depends on whether you are measuring saturated or unsaturated hydraulic conductivity. It can be difficult to try and do this for saturated hydraulic conductivity in the field. In theory, if you took a sample from the field and measured this in the lab, horizontal vs. vertical should be the same in terms of hydraulic conductivity. Hydraulic conductivity is independent of whether the flows are vertical or horizontal because these components are corrected for. If you want to measure unsaturated hydraulic conductivity in the field and look at how it changes in the horizontal vs. vertical position, this could potentially be done with tensiometers and water content sensors positioned in a grid to look at the movement of water and change in water potential. Find more information on how to measure hydraulic conductivity here.
- Hydraulic conductivity - GENERAL - MINI DISK INFILTROMETER What influence do high soil temperatures associated with forest fires have on short term unsaturated conductivity?
Because of the hydrophobicity effect from the high temperatures associated with forest fires, I expect you would see a significant impact on the unsaturated hydraulic conductivity of the soil. There are experts who have done work in this area. Researchers at the US Forest Service would be a great sounding board for this question. Pete Robichaud, in particular, might have some thoughts on this topic. We’ve highlighted his forest fire research here.
- Hydraulic conductivity - SATURO - GENERAL - MINI DISK INFILTROMETER Lab Ks measurements move from the bottom to the top. Is Ks similar if water goes from the top to the bottom of a sample?
As long as the calculations are done correctly there shouldn’t be a difference if water is percolated from the bottom or the top of the sample.
- Hydraulic conductivity - GENERAL What is the difference between liquids like water (polar liquids) and oils (non-polar or organic liquids) in terms of diffusion and the fate of liquids in soil. Does oil have different conductivity variables to measure?
There will be a difference in how non-polar liquids move through soil. The interaction with the soil surfaces will be different along with the differences in viscosity. There are ways to model these liquids, but you will need to consult an expert in this area.
- Hydraulic conductivity - SATURO - GENERAL Soil with rock fragments is a common soil type but difficult to measure with traditional methods. What do you suggest?
Rock fragments can make things difficult when trying to measure hydraulic conductivity. If it is possible to avoid the rocks, that is the best approach. This will depend on the size of the rock fragments. If you are measuring in a gravelly site, you can still use traditional methods, but you will likely need to repair the ring edges more regularly as they will get bent and dinged frequently. If you have very large fragments, avoid the large rocks by measuring in a smaller area or by trying to encompass the large rocks within the infiltrometer. In some cases, a borehole approach might work better for these situations.
- Hydraulic conductivity - SATURO - GENERAL In preparing for an infiltrometer test, I’m thinking of statistical significance so would like multiple sites. How far apart should my test holes be?
Some of this depends on the soil variability at the site. Typically, we take measurements in triplicate at a single site. We then try to cover the expected variability at the site. This could mean somewhere around 3 to 12 measurement sites within a location. One way to approach this is to start with three sites and see what the variability looks like.
- 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.
- Hydraulic conductivity - GENERAL What is the relationship between soil/regolith profile and hydraulic conductivity in explaining the overall hydrology of the terrain?
Hydraulic conductivity through a profile is a small component used to explain the overall hydrology of the terrain. You need to understand hydraulic conductivity in order to understand how the water is going to move through the soil. But, if you want to understand this across a large landscape, you will need to know how the soil varies and how the hydraulic properties change across the site.