Search results for 'hydraulic conductivity'

Mar 6

New Infiltrometer Helps City of Pittsburgh Limit Traditional Stormwater Infrastructure (Part 2)

To save the aesthetics of Dellrose Street, an aging, 900 ft. long, brick road, the city of Pittsburgh wanted to limit traditional stormwater infrastructure (see part 1). Jason Borne, a stormwater engineer for ms consultants and his team decided permeable pavers was a viable option, and used two different types of infiltrometers to determine soil infiltration potential. Here’s how they compared.

Looking down the street where researchers are doing their installation

Setting up the infiltrometers.

Shortened Test Times Allow Design Changes on the Fly

Though most of the subsoil was a clay urban fill, there was a distinct transition between that clay material to a broken shale/clay mixture. Borne says, “After excavation, it rained, and we saw that the water was disappearing through the broken shale/clay material. When we did the infiltration tests, the broken shale/clay showed a higher infiltration potential than the clay fill material. That led us to modify the design of the subsurface flow barriers based on specific observed infiltration rates of the subsoils. Where the tests showed higher hydraulic conductivity values, we were able to rely on infiltration entirely to remove the water from behind the check dams.” Borne adds that in the areas where infiltration was poor, they augmented infiltration with a slow release concept. “We put some weep holes in the flow barrier and let the water trickle out down to the next barrier and so on. Basically, the automated SATURO infiltrometer allowed us to do many tests in a short amount of time to establish a threshold of where good infiltrating soils and poor infiltrating soils were located. This enabled us to change the design on the fly. The double ring infiltrometer takes significantly more time to do a test, and time is of the essence when the contractor wants to backfill the area and get things moving. It was nice to have a tool that got us the information we needed more rapidly.”

Image of a SATURO double ring infiltrometer

SATURO Infiltrometer

How did the Double Ring and SATURO Compare?

Borne says the SATURO Infiltrometer was faster and reduced the possibility of human error. He adds, “We liked the idea of it being very standardized. The automated plot of flux over time was also of great interest to us, because we could see a trend, or anomalies that might invalidate the results we were getting. The double ring infiltrometer takes a long time to achieve a state of equilibrium, and it’s hard to know when that occurs. You’re following the Pennsylvania Department of Environmental Protection suggested guidelines, but they’re very generalized. To me it doesn’t suit all situations. What we found with the SATURO infiltrometer is it records information at very discreet intervals, plots a curve of the flux over time, and when it levels out, you basically achieve equilibrium. You get to that state of equilibrium faster. There’s a water savings, but there’s also a time savings. And there’s the satisfaction of getting standardized results rather than the possibility of each technician applying the principles in a slightly different way, as they might with the double ring infiltrometer.”

Borne and his team were ultimately able to prepare a permeable paver street design which allowed for the exclusion of traditional storm sewer infrastructure, reducing both capital costs and long-term maintenance life cycle costs. The permeable paver concept is intended to provide a template for the city of Pittsburgh to apply to the future reconstruction of other city streets.

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Feb 27

New Infiltrometer Helps City of Pittsburgh Limit Traditional Stormwater Infrastructure

Though difficult and expensive to restore, the brick-paved streets that still exist in some Pennsylvania neighborhoods are a treasure worth preserving, according to the City of Pittsburgh. Dellrose Street, an aging, 900 ft. long, brick road, was in need of repair, but the city of Pittsburgh wanted to limit traditional stormwater infrastructure, such as pipes and catch basins.

Dellrose Street permeable paver system

To save the aesthetics of the neighborhood, they hired ms consultants, inc. to design a permeable paver solution for controlling stormwater runoff volumes and peak runoff rates that would traditionally be routed off-site via storm sewers. Jason Borne, a stormwater engineer for ms consultants who worked on the project says, “What we try to do is understand the in situ infiltration potential of the subsoils to determine the most efficient natural processes for attenuating flows; either through infiltrating excess water volume back into the soil or through slow-release off-site.” He used the SATURO Infiltrometer to get an idea of how urban fill material would infiltrate water.

Green Infrastructure Aids Natural Infiltration

As Borne and his team investigated what they could do to slow down the runoff, they decided permeable pavers would be a viable solution. He says, “There’s not much you can do once you put in a hardened surface like a pavement. Traditional pavement surfaces accelerate the runoff which requires catch basins and large diameter pipes to carry the runoff off-site. We were interested in investigating what some of the urban subsoils or urban fill would allow us to do from an infiltration perspective. As we started looking at some of these subsoils, we decided a permeable paver system would be ideal for this particular street.”

Researchers install a subsurface flow barrier

Subsurface flow barrier installation

Infiltrometers Determine Natural Infiltration Potential

Once the water flowed into the aggregate, the team began to figure out ways to slow it down and promote infiltration. Borne says, “Basically we came up with a tiered subsurface flow barrier system. We had about 60 concrete flow barriers across the subgrade within the aggregate base of the road. We needed so many because the longitudinal slope of the road was fairly significant. Behind each of these barriers we stored a portion of the stormwater that would typically run off the site. The ideal was to remove the stored water through infiltration—to get it down to the subgrade and away, so we used infiltrometers to help us establish where we could maximize infiltration and where we might need to rely on other management methods.”

A Need for Faster Test Times Inspires a Comparison

Borne says that USDA soil surveys are too generalized for green infrastructure applications in urban areas and only give crude approximations of the soil hydraulic conductivity. Understanding the best way to promote natural infiltration requires a very specific infiltration rate or hydraulic conductivity for the location of interest. He says, “The goal is to excavate down to the desired elevation before construction and find out, through some kind of device what the infiltration potential of the subsoil is. Typically we use a double ring infiltrometer, but it’s a very manual device. We’re constantly refilling water, and it requires us to be on-site and attentive to what’s happening. We can’t really multitask, especially in areas of decently infiltrating soils where the device might run out of water in 30 minutes or less. So, in the interest of saving water and time, we used the automated SATURO infiltrometer and the manual double ring infiltrometer concurrently for comparison purposes.”

Next week: Find out how the two infiltrometers compared.

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Dec 26

1 Comment

How to Measure Water Potential

In the conclusion of our 3-part water potential series (see part 1), we discuss how to measure water potential—different methods, their strengths, and their limitations.

Image of a mountain with a little snow on the top

Vapor pressure methods work in the dry range.

How to measure water potential

Essentially, there are only two primary measurement methods for water potential—tensiometers and vapor pressure methods. Tensiometers work in the wet range—special tensiometers that retard the boiling point of water (UMS) have a range from 0 to about -0.2 MPa. Vapor pressure methods work in the dry range—from about -0.1 MPa to -300 MPa (0.1 MPa is 99.93% RH; -300 MPa is 11%).

Historically, these ranges did not overlap, but recent advances in tensiometer and temperature sensing technology have changed that. Now, a skilled user with excellent methods and the best equipment can measure the full water potential range in the lab.

There are reasons to look at secondary measurement methods, though. Vapor pressure methods are not useful in situ, and the accuracy of the tensiometer must be paid for with constant, careful maintenance (although a self-filling version of the tensiometer is available).

Here, we briefly cover the strengths and limitations of each method.

Vapor Pressure Methods:

The WP4C Dew Point Hygrometer is one of the few commercially available instruments that currently uses this technique. Like traditional thermocouple psychrometers, the dew point hygrometer equilibrates a sample in a sealed chamber.

WP4C Dew Point Hygrometer

A small mirror in the chamber is chilled until dew just starts to form on it. At the dew point, the WP4C measures both mirror and sample temperatures with 0.001◦C accuracy to determine the relative humidity of the vapor above the sample.

Advantages

The most current version of this dew point hygrometer has an accuracy of ±1% from -5 to -300 MPa and is also relatively easy to use. Many sample types can be analyzed in five to ten minutes, although wet samples take longer.

Limitations

At high water potentials, the temperature differences between saturated vapor pressure and the vapor pressure inside the sample chamber become vanishingly small.

Limitations to the resolution of the temperature measurement mean that vapor pressure methods will probably never supplant tensiometers.

The dew point hygrometer has a range of -0.1 to -300 MPa, though readings can be made beyond -0.1 MPa using special techniques. Tensiometers remain the best option for readings in the 0 to-0.1 MPa range.

Secondary Methods

Water content tends to be easier to measure than water potential, and since the two values are related, it’s possible to use a water content measurement to find water potential.

A graph showing how water potential changes as water is adsorbed into and desorbed from a specific soil matrix is called a moisture characteristic or a moisture release curve.

Example of a moisture release curve.

Every matrix that can hold water has a unique moisture characteristic, as unique and distinctive as a fingerprint. In soils, even small differences in composition and texture have a significant effect on the moisture characteristic.

Some researchers develop a moisture characteristic for a specific soil type and use that characteristic to determine water potential from water content readings. Matric potential sensors take a simpler approach by taking advantage of the second law of thermodynamics.

Matric Potential Sensors

Matric potential sensors use a porous material with known moisture characteristic. Because all energy systems tend toward equilibrium, the porous material will come to water potential equilibrium with the soil around it.

Matric Potential Sensor

Using the moisture characteristic for the porous material, you can then measure the water content of the porous material and determine the water potential of both the porous material and the surrounding soil. Matric potential sensors use a variety of porous materials and several different methods for determining water content.

Accuracy Depends on Custom Calibration

At its best, matric potential sensors have good but not excellent accuracy. At its worst, the method can only tell you whether the soil is getting wetter or drier. A sensor’s accuracy depends on the quality of the moisture characteristic developed for the porous material and the uniformity of the material used. For good accuracy, the specific material used should be calibrated using a primary measurement method. The sensitivity of this method depends on how fast water content changes as water potential changes. Precision is determined by the quality of the moisture content measurement.

Accuracy can also be affected by temperature sensitivity. This method relies on isothermal conditions, which can be difficult to achieve. Differences in temperature between the sensor and the soil can cause significant errors.

Limited Range

All matric potential sensors are limited by hydraulic conductivity: as the soil gets drier, the porous material takes longer to equilibrate. The change in water content also becomes small and difficult to measure. On the wet end, the sensor’s range is limited by the air entry potential of the porous material being used.

METER Tensiometer

Tensiometers and Traditional Methods

Read about the strengths and limitations of tensiometers and other traditional methods such as gypsum blocks, pressure plates, and filter paper here.

Choose the right water potential sensor

Dr. Colin Campbell’s webinar “Water Potential 201: Choosing the Right Instrument” covers water potential instrument theory, including the challenges of measuring water potential and how to choose and use various water potential instruments.

Take our Soil Moisture Master Class

Six short videos teach you everything you need to know about soil water content and soil water potential—and why you should measure them together. Plus, master the basics of soil hydraulic conductivity.

Watch it now—>

Download the “Researcher’s complete guide to water potential”—>

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Dec 19

1 Comment

Water Potential: The Science Behind the Measurement (Part 2)

In the second part of this month’s water potential series (see part 1), we discuss the separate components of a water potential measurement. The total water potential is the sum of four components: matric potential, osmotic potential, gravitational potential, and pressure potential. This article gives a description of each component. Read the article here…

Visualize Matric Potential

Next Week: Learn the different methods for measuring water potential and their strengths and limitations.

Take our Soil Moisture Master Class

Watch it now—>

Download the “Researcher’s complete guide to water potential”—>

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Dec 11

2 Comments

Secrets of Water Potential: Learn the Science Behind the Measurement

This month in a 3 part series, we will explore water potential —the science behind it and how to measure it effectively.

Pouring water into a glass with ice around the glass

To understand water potential, compare the water in a soil sample to water in a drinking glass.

Water Potential: a Definition

Read the article here…

Next week learn about the four components of water potential—osmotic potential, gravitational potential, matric potential, and pressure potential.

Take our Soil Moisture Master Class

Watch it now—>

Download the “Researcher’s complete guide to water potential”—>

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Apr 25

The Tensiometer: Micro-sized

A strand of a spider’s web is 5 micrometers in width. Microelectromechanical systems (MEMS) devices range in size from 20 micrometers to one millimeter. That’s the incredibly small size of the components used in the tensiometer being developed by PhD candidate, Michael Santiago, and his collaborators, professors Abraham Stroock and Alan Lakso at Cornell University.

Spider wed with dew water on the strands

MEMS devices can be as small in width as 4 strands of a spider’s web.

The engineer/research team is using MEMS technology to develop a miniature tensiometer (microtensiometer) that has a 100 times larger range than existing tensiometers, is stable for months, communicates digitally, and can be embedded into plant stems to directly measure plant water potential.

Existing Tensiometer Limitations:

Water potential is the best measure of a plant’s hydration relative to growth and product yield. Unfortunately, directly measuring water potential in plant tissue is only possible through labor-intensive, destructive methods such as the leaf pressure bomb and stem psychrometer. A common alternative is to use ‘set-and-forget’ soil tensiometers to measure soil water potential as a proxy for plant water potential, but this method is unreliable for plants with high hydraulic resistance (vines and woody species), where plant water potential is often much less than the water potential in soil. Although soil tensiometers are very accurate and simple to use, they can be large and bulky, and cavitate as soils dry.

A 25 cent coin next to a prototype microtensiometer

Prototype microtensiometer made with MEMS components.

Solution:

The Cornell University research team wants to improve the design of the tensiometer so it can be used in the field for applications such as continuously monitoring and controlling plant water potential in vineyards to consistently produce high-quality wine grapes with an exact flavor/aroma profile. Santiago says, “We’ve basically miniaturized a tensiometer using microchip technology to the point where it’s this tiny chip inside a wafer. Because of the way we fabricated it, we are hoping to make it an embeddable tensiometer that can go in anywhere and measure tension down to about -100 bars (-10 MPa).”

Developing and Calibrating

Santiago is using a chilled mirror hygrometer to produce solutions of specific water potential to test, calibrate, and characterize the microtensiometer. He comments, “We’ve been testing it in osmotic solutions. We use the water potential meter for calibrating a solution of PEG (polyethylene glycol), and then we measure it with the tensiometer.”

One hurdle the team has to overcome is finding a membrane that keeps small molecules and ions out of the tensiometer pores: these pollute the water inside the tensiometer and cause measurement errors. Santiago explains, “Our solution right now is to test in solutions of large molecules, such as PEG of 1400 molecular weight. The tensiometer pores are about 3-4 nanometers, extremely small, but small molecules, such as sugars and salts, can still get through. It’s not a problem for the short term because we are directly submerging into solutions of just water and large molecules, but our goal is to go into the environment and insert the tensiometer into soils and plant stems where small molecules are ubiquitous, so we’ll have to find a membrane that works and can handle field testing.”

The team has been experimenting with materials such as Gore-Tex and reverse osmosis membranes [M5] [M6] hoping to find a membrane that allows water through and keeps ions out, but does not slow the measurement.

Researchers want be able to insert the device directly into plant xylem.

What’s Next?

Santiago says the calibrations have worked well. Now the challenge will be putting the tensiometer into different environments such as soil, concrete, and plants. For example, they want be able to insert the device directly into plant xylem, which will require a seal so water is not exiting the system. And that’s not the only complication. Santiago explains, “We are getting ready to do some testing in soils. The challenge will be getting good data because soil can be really heterogeneous, and we have this sensor with a much larger range than the usual tensiometer. So what do we compare it with? That’s going to be a bit of a challenge.” Santiago says the next few months will be spent getting into some different materials and obtaining some initial publishable data.

Take our Soil Moisture Master Class

Watch it now—>

Download the “Researcher’s complete guide to water potential”—>

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Apr 7

Green Roofs—Do They Work? (Part II)

Innovative soil scientist, John Buck, and his team have discovered that green roofs have more capacity than people imagined (see part I). Below are some of the challenges he sees for the future, and the type of measurements he suggests researchers take, as they continue to validate the effectiveness of these urban ecosystems.

Green and whited plant on a garden rooftop with orange rocks

A green roof is essentially a garden on a roof, but rather than growing plants in soil, installers use a synthetic substrate made of expanded shale, expanded clay, crushed brick, or other highly porous, lightweight material.

New Challenges for Green Roofs

Green roof results are promising, but they present a new challenge: making sure the plants have enough water. The crux of the challenge is that the lightweight, expanded shale/clay substrate material, the standard in green roof design, does a good job of soaking up the water, but has some peculiar properties that are unlike typical soils. Specifically, the expanded shale and expanded clay media tend to be dominated by sand and fine gravel-sized particles that provide a high proportion of macropores, but the interior porosity of the large particles is dominated with micropores. That pore size distribution leads researchers to two important questions— How much water will be readily available for plant growth? And, will the unsaturated hydraulic conductivity be adequate to avoid starving the roots under high-evaporative demand by allowing water to flow to roots from the bulk soil? These are critical questions as green roof technologies continue to evolve.

Researchers wonder, will the unsaturated hydraulic conductivity be adequate to avoid starving the roots under high-evaporative demand.

Measurements Required for Green Roof Validation

Still, Buck has learned a great deal from his work. Considering the wild spatial distribution of summer storms, quantitative green roof performance studies require that rainfall be measured locally. Monitoring of soil volumetric moisture content measurements in concert with rainfall and soil lysimeter measurements of drainage, reveal the degree of total and capillary saturation, drainage rate, and porosity available for storage. Soil water potential sensors, placed within the capillary fringe of water ponded over subsurface drainage layers, can provide useful insights regarding the dryness of the drainage layer and overlying soil, as well as the available storage of stormwater within the drainage layer.

Direct measurement of soil drainage using lysimeters is a key supplemental measurement on green roof performance quantification projects because there is an unmeasured component of water storage where drought-resistant alpine succulents (typically Sedum species) are used on green roofs. The Sedum plants can absorb up to 10 mm of rainfall equivalent in their plant tissues.

Plants poking out of the soil in front of a house

Measurement of soil drainage using lysimeters is a key supplemental measurement on green roof performance quantification projects.

Other Projects and Future Plans

At ground level, Buck is quantifying the performance of intensive stormwater infiltration areas known as rain gardens, bioretention areas, or more generically, infiltration-based stormwater best management practices (Infiltration-based BMPs). When monitoring infiltration-based stormwater BMPs, Buck has used similar tools to those used on green roofs, but has added water-level sensors and piezometers. Buck has found that ancillary measurements of electrical conductivity, often available on water content sensors, along with surface and pore water sampling, can be used to document transformations taking place in infiltration systems. These measurements now combine to show that green roofs and infiltration-based BMPs are indeed making a difference to urban environments and contributions to CSOs. The challenge now is how to implement this technology more widely. But, with the validation now in hand, that job should be quite a bit easier.

Download the “Researcher’s complete guide to water potential”—>

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Mar 23

1 Comment

Can Wastewater Save The United Arab Emirates’ Groundwater? (Part II)

With very little recharge and irrigation comprising 75% of groundwater use, natural water resources in the United Arab Emirates region are disappearing fast (see part I). Wafa Al Yamani and her PhD advisor, Dr. Brent Clothier, are investigating using treated sewage effluent and groundwater for irrigating the desert forests along UAE motorways.

Abu Dhabi

Infiltrometers Predict Dripper Behavior:

Wafa and her team used what they call, “the Ankeny twin head method” for site evaluation with infiltrometers, and they’ve been able to use it to predict dripper behavior. They begin with the head at -60 mm, do a series of measurements to measure steady infiltration, and repeat the process at -5 mm. They use those measurements to solve Woodings equation which has two unknowns: saturated hydraulic conductivity and capillarity. Dr. Clothier says, “We’ve done it at two heads, and we can use Woodings equation to solve for the slope of the exponential conductivity curve. Hence, I can predict with time, the movement of the wetting front away from the dripper. That’s been very useful to work out what volume of soil we’re wetting. It tells us if we should have one or two drippers. In this forest, we think we can get away with two drippers because if they irrigate for two hours, the radius of the wet front will be 20 cm, and the depth will be about 40 cm, which is a sufficient volume of water for the tree roots.” Dr. Clothier says they also constructed a small dyke around the drippers so they could contain the water inside the drip zone in case of hydrophobicity or uneven sand.

researcher recording data while sitting on the floor

Wafa on site, using the twin head method.

Treated Effluent Resolves Salinity Issues

Historically, the UAE pumped their sewage effluent into the Arabian Gulf, but recently, there has been a shift toward seeing it as a valuable water resource, not only for the desert forest, but for irrigation of fruit crops and date palms. Dr. Clothier says, “Once we started getting our results we realized we were irrigating with groundwater that had high salinity, about 10 dS/m, and that treated sewage effluent had only 0.5 dS/m. This was an important discovery because with the high salinity groundwater, you have to over-irrigate to maintain a salt leaching fraction. However, when we apply the treated sewage effluent, we immediately see a response in the trees because it has 1/20th of the salt load.”

Dr. Clothier says that there is one problem with the trees responding so well to the sewage effluent. The treated sewage effluent makes the trees grow taller and faster, so if the ecosystem service you want from the desert forest is that they’re 4-6 meters high, it becomes an issue. He adds,”This is actually a positive problem, because we can now induce deficit irrigation, thereby creating a larger resource of treated sewage effluent in order to irrigate far more forests.”

Large white irrigation tanks sitting in sand in the desert

Researchers irrigated with water from these tanks which stored groundwater and treated sewage effluent.

What’s The Future?

Dr. Clothier says they started with a pilot study in the UAE in 2014, and it was so successful that they ended up with two fully-funded four-year projects, one on treated sewage effluent, and one investigating the irrigation of date palms. He says they have another 3 ½ years of work in the UAE on these projects, and in the end, their goal is to develop a model for forestry irrigation and soil salinity management, along with developing capability for the measurement and modeling of irrigation impacts on sustainable forestry. They have recently developed a prototype of a computerized decision support tool for irrigation which will provide sustainable irrigation advice to optimize water use. The support tool takes into account the need to maintain salt leaching, and actual irrigation records can be entered to enable real-time use.

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Feb 11

1 Comment

Estimating Relative Humidity in Soil: How to Stop Doing it Wrong

Estimating the relative humidity in soil? Most people do it wrong…every time. Dr. Gaylon S. Campbell shares a lesson on how to correctly estimate soil relative humidity from his new book, Soil Physics with Python, which he recently coauthored with Dr. Marco Bittelli.

Radioactive waste buried in steel containers will corrode if the humidity is too high.

A number of years ago a former student told me of a meeting he had with some engineers establishing a low-level radioactive waste repository in a desert area. The waste was to be buried, and at least some of it was in steel containers which would corrode if the humidity was too high. The engineers assumed the humidity in the soil would be pretty low because it was a desert, but they didn’t know how low. So, what is the relative humidity in soil? That sounds like it would be a hard thing to find out without measuring it, but it isn’t. Let’s apply a little physics to see what we can find.

The energy required to create an infinitesimal volume of water vapor can be found using the first law of thermodynamics. For an adiabatic system

where dE is the energy required, p is the pressure, and dV is the volume change.

The Boyle-Charles law, which gives the pressure-volume relationship for a perfect gas, is

where n is the number of moles of gas, R is the universal gas constant, and T is the kelvin temperature. Rearranging terms and taking the derivative of both sides gives

This equation can be substituted for dV in the first equation, giving

The total energy required to go from a reference vapor pressure, po (the vapor pressure of pure water) to the vapor pressure of the water in the soil, p is

We can divide both sides by the mass of water. The left side then becomes the energy per unit mass of water in the soil, which we call the water potential. On the right side, the number of moles per unit mass is the reciprocal of the molecular mass of water, and the ratio of the vapor to the saturation vapor pressure is the relative humidity hr so the final equation is

We can rearrange this and take the exponential of both sides, giving

In the second version of the equation the molecular mass of water, the gas constant and the temperature (298K) have been substituted.

We can use this equation to find the range of humidities we would expect in soil. When soil is very wet, the water potential is near 0, so the humidity is exp(0) = 1. At the dry end, the soil is dried mainly by plant water uptake. Even desert soils support some vegetation. The soil near the surface will be dried by evaporation, but a few decimeters below the surface the lowest water potentials are those to which plants can dry them. The nominal permanent wilting point (lower limit of plant available water) is -1500 J/kg. Desert vegetation can extract water to lower potentials. If we say their lower limit is -2500 J/kg, then the humidity is

so the relative humidity in the soil is around 98%. Sagebrush can go lower than -2500 J/kg. We measured -7000 J/kg under it at the end of the growing season. Even that, though, is around 95% humidity.

The conclusion is that the humidity in the soil is always near saturation, except in a shallow evaporation layer near the surface. I don’t remember what the engineers were expecting. I think anything above 60 or 70% was going to be a disaster for corroding the steel containers. I don’t know whether they believed the calculations or just went on thinking that desert soil is dry.

Take our Soil Moisture Master Class

Watch it now—>

Download the “Researcher’s complete guide to water potential”—>

Download the “Researcher’s complete guide to soil moisture”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Dec 11

2 Comments

Reforestation in the Philippines (Part 1)

In the mountainous Benguet province of the Philippines, farmers grow up to three crops of vegetables a year. Their mountain vegetable farms exist at the expense of original forest cover, causing tremendous erosion difficulties. To counteract erosion and preserve the watershed as well as promote reforestation, the Philippine government issued a mandate: farmers must find alternatives that restore the watershed or lose their land.

Rice terraces in the Philippines

An Agroforestry Alternative

Loreca Stauber is no scientist, but she loves Benguet, and a letter from her friend, a scientist living in the Philippines, inspired her with the vision of teaching farmers to reforest the mountains and grow vegetables amongst the trees.

Her friend writes, “We envision mountain farms as forest ecosystems whose primary social responsibility to the communities around and below is to be part of responsible watersheds that court, catch, store and gradually share water. We see mountain farms that are not prone to soil erosion or leaching: cultivated with minimal chemical inputs and tillage that will allow the natural buildup of biomass, organic matter, helpful organisms and fauna. We think of forest ecosystems that may not make millionaires of its farmers for one generation and heavy debtors even before the next. Rather, we envision forest farm ecosystems that are self-sufficient and self-sustaining. We are working on demonstrating forest ecosystems that can substitute for monocrop vegetable farms that deplete and leach the soil, pollute watersheds and are self-destructing.”

Realizing the problem in the Philippines could be solved by reforestation, Loreca emailed Dr. Anthony S. Davis, Tom Alberg and Judi Beck Chair in Natural Resources in the University of Idaho’s Department of Forest, Rangeland, and Fire Sciences. The U of I operates a 100-year-old nursery specializing in growing hardy tree seedlings. Dr. Davis recalls, “The email she sent me said, “I think you should do something about this,” and I thought, “Actually I agree. I think we should do something about this. So we began to screen the idea, asking: are there partners? Is it a good idea? Does it fit with this little thing that we do really well, which is essentially teaching people how to grow tree seedlings, and is there an educational component that’s valuable for our students? When those check boxes lined up, then it was a matter of taking advantage of that opportunity and seeing where it could go.”

Forested mountains in the Philippines

Determining What Already Works

Together, they and other partners started a program in which U of I students went overseas to teach the people of Benguet how to grow trees, with the goal of moving the land toward agroforestry. They wanted to grow a forest ecosystem (trees, shrubs, and ground cover) along with annual crops. Kea Woodruff, former U of I Nursery Production and Logistics Associate, now at Harvard University, traveled to the Philippines with an interdisciplinary team of undergraduate and graduate students to look at what agroforestry projects were already working and to conduct a needs assessment. She says, “I saw a wide variety of landscapes in the areas that we were. One woman decided on her own that she was going to practice agroforestry, and people come and view her land as a demonstration site. It has mature bamboo, coffee trees, and mature Benguet pine. It really looks like what you would expect the native forest to look in an area like the Philippines.”

Kea said there were also intermediate sites where there are Benguet pines and some coffee with row crops blended in, such as strawberries and squash. She adds, “There’s clearly great potential to grow different species on these lands if we can help figure out the best way to use the resources that are available.”

Next week: Learn how partners in the project have been able to use native resources in the quest to reforest erosion-plagued Benguet.

Take our Soil Moisture Master Class

Watch it now—>

Download the “Researcher’s complete guide to soil moisture”—>

Download the “Researcher’s complete guide to water potential”—>

Get more information on applied environmental research in our

LinkedIn Facebook Messenger X Reddit Threads Email Copy

Measuring and Modeling the Environment

Search results for 'hydraulic conductivity'

Shortened Test Times Allow Design Changes on the Fly

How did the Double Ring and SATURO Compare?

Green Infrastructure Aids Natural Infiltration

Infiltrometers Determine Natural Infiltration Potential

A Need for Faster Test Times Inspires a Comparison

How to measure water potential

Vapor Pressure Methods:

Secondary Methods

Matric Potential Sensors

Tensiometers and Traditional Methods

Choose the right water potential sensor

Take our Soil Moisture Master Class

Visualize Matric Potential

Take our Soil Moisture Master Class

Water Potential: a Definition

Take our Soil Moisture Master Class

Existing Tensiometer Limitations:

Solution:

Developing and Calibrating

What’s Next?

Take our Soil Moisture Master Class

New Challenges for Green Roofs

Measurements Required for Green Roof Validation

Other Projects and Future Plans

Infiltrometers Predict Dripper Behavior:

Treated Effluent Resolves Salinity Issues

What’s The Future?

Take our Soil Moisture Master Class

An Agroforestry Alternative

Determining What Already Works

Take our Soil Moisture Master Class