Posts from the ‘Canopy’ Category

Dec 5

What plant hydraulics tell us about drought response

Trees are merchants; they sell water to the atmosphere in exchange for the CO₂ they need to photosynthesize sugars. The exchange rate or ‘water-use efficiency’ that drives the plant carbon-water market place is a function of atmospheric CO₂ concentrations. Thus, theoretically human carbon emissions, which have increased atmospheric CO₂ by 40% since 1850, should increase plant water use efficiency, resulting in “CO₂ fertilization” of our forests and crops.

La Plata Mountains, where the study gradient is located

However, evidence for CO₂ fertilization is extremely mixed. That’s why Leander Anderegg, postdoctoral fellow at UC Berkeley, and his research team are performing a two-step experiment to determine if increased atmospheric CO₂ conditions increase plant water-use efficiency. The team is leveraging a natural elevation gradient in temperature, vapor pressure deficit, and precipitation on a southwestern Colorado mountain to understand:

How much physiological variation is on a single mountain slope between two species
How that variation ultimately affects the potential for CO₂ fertilization and differential vegetation responses to rising CO₂

For five years, the team has worked on quantifying how two tree species (Ponderosa Pine and Trembling Aspen) can shift their physiology going from low elevation (hot, high vapor pressure deficit environments) up to high elevation (wet, cooler, low vapor pressure deficit environments). They want to understand what that means for each species’ water relations, drought vulnerability, and biogeography in a drying and warming climate.

Quantifying weather parameters

Anderegg and his team use METER all-in-one weather stations to quantify exactly how much the local environment changes from the bottom to the top of the mountain. Anderegg says he’s been surprised at how influential vapor pressure deficit changes are on the tree species. He says, “When we compare Aspens to Ponderosas, we’ve found that the difference in atmospheric demand is a big part of the story, particularly in how they respond to drought stress. There is more atmospheric demand at the bottom of the mountain. So one key objective was to quantify how much drier the air was during the peak mid-summer dry down for most of the species. This was critical then to infer how stomata were responding to that gradient and water stress. It’s really difficult in these wide field plots to actually measure transpiration. But with physiological measurements of leaf water potential, hydraulic conductivity, and the vapor pressure deficit from relative humidity sensors, we could then infer how open the stomata were.”

Coring a ponderosa to measure its growth rate

Anderegg used a pressure chamber to measure leaf water potential and also did a lot of shotgun sampling to measure the hydraulic conductivity in twigs. He describes the process, “I went out at 3 am with a 20 gauge shotgun loaded with birdshot to shoot off branches. We pulled water through the branches by applying a vacuum to a pressure chamber and then inserting one end of the branch. To get the hydraulic conductivity of the branch, we measured how quickly the water moved into the chamber.” (Kolb et al 1996)

Vapor pressure deficit was surprising

Anderegg says vapor pressure deficit changes across the elevation gradient were much stronger than he expected. He says, “It was pretty impressive that as you drove up this elevation gradient, the vapor pressure deficit differed by approximately 1.5 kPa. In the crop realm, a vapor pressure deficit of 2 kPa is pretty intense, but we went from a bit over 1 kPa near the top of the mountain to more like 3 kPa down at the drier bottom, which translates to a remarkably different water-use efficiency.

Two species—two adaptation strategies

When asked what they’ve learned, Anderegg says the difference between the two tree species is pretty amazing. “We’ve seen that the two species have extremely different responses to drought stress. Aspen keeps its stomata open, even at the bottom of the mountain where it’s really dry. It just alters its hydraulic system to try and keep up with it. The Ponderosa, however, does not alter its hydraulic system. It just closes its stomata until it rains in the fall.”

A dead Aspen tree next to a living Ponderosa tree

An aspen that died following a drought while it’s neighboring ponderosa lived

Anderegg adds that the two different water relations strategies line up with the type of biogeographical shifts occurring in the two species as the Southwest dries out. He says, “Aspen is sort of a ‘grin-and-bear-it’ species that toughs out drought while Ponderosa is a ‘sit it out’ sort of species. For the last 15 years, the Aspen have been creeping uphill but not gradually. Intermittent droughts are slowly trimming the driest Aspen up the hill in fits and starts. Ponderosa are better at dealing with extreme droughts because they preserve their hydraulic systems. We have not seen mortality pushing the Ponderosa uphill. However, there’s essentially no Ponderosa recruitment (new tree starts) at the bottom of the hill, and the growth rates of adults are a quarter of the rates at the top of the hill. So we think the Ponderosa will move uphill following mean climate change and not in fits and starts. They’ll gradually die off at the bottom and not be replaced by young recruits which will cause them to move uphill in a more gradual manner.”

Dying Aspen tree in the middle of a low elevation Aspen stand

Dying aspens in the middle of a low elevation aspen stand

Transitioning toward the future

In the years ahead, Anderegg hopes to move into the second phase of the experiment: testing how these two species will respond to CO₂ fertilization. He says, “We need to make these measurements over multiple years and many environmental conditions to start to get at how much plasticity any individual plant can manifest (plasticity is the amount that a plant can change its physiology in response to climate change. So if this condition happened, how likely is the plant to respond in a particular way over time) and what the long term trajectories are in these hydraulic traits. We’ve gotten measurements at the height of a significant drought and then another medium year following that drought. We want to transition toward a long-term monitoring perspective that hopefully will give us the information we need to start thinking about how CO₂ then plays in.”

You can learn more about Leander Anderegg’s research here: ldlanderegg.com

Reference:

Kolb KJ, Sperry JS, Lamont BB (1996) A method for measuring xylem hydraulic conductance and embolism in entire root and shoot systems. Journal of Experimental Botany. 47:304, pg 1805-1810

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Apr 12

Why mesonets make weather prediction more accurate

The staggering cost of Montana’s “flash drought”

Some people figured it was climate change. One statistician said it was a part of a cyclical trend for poor crop years. Whatever the cause, the 2017 flash drought that parched the entire state of Montana and most of South Dakota, severely impacted the profitability of ranchers and farmers. In western Montana, fires burned some of the largest acreages in recent history. It resulted in one of the biggest wildfire incident reports (over one-million acres) and caused virtually 100% crop loss in northeastern Montana. The U.S. Dept. of Agriculture estimated the crop loss to be in the hundreds of millions of dollars, and one question was on everybody’s mind—why did no one see it coming?

Figure 1. Montana drought conditions August 2017 (Source: Montana State Library website: https://mslservices.mt.gov/Geographic_Information/Maps/drought/)

Getting the right weather data

The 2017 Montana Dept. of Natural Resources and Conservation spring drought report indicated plenty of water: “By the end of the month, almost all drought concern was removed from the state, with the exception of Wibaux and Fallon Counties….As of May 9, 2017, Montana was 98.45% drought free.” But in late May, an abrupt shift in weather conditions led to one of the hottest, driest summers on record.

The problem, says Kevin Hyde, Montana State Mesonet Coordinator, lies not only in the need for more weather data but in obtaining the right kind of data. He says, “One of the reasons drought was missed was because we’re still thinking you measure drought by snowpack and how much water is in the river, which is really great if you’ve got water rights. But we’ve got a lot of dryland out there.”

In addition to weather monitoring, Hyde is a big proponent of adding soil moisture and NDVI measurements to each of the Montana Mesonet stations he oversees. He says, “The conventional weather station only measures atmospheric conditions. But ultimately, to make any decisions, we’ve got to know not just how much water comes into the system, but how much goes into the soil. And even that’s not enough…because what we really need to know is how the water situation is going to affect plants.”

Hyde says more data are needed to warn growers and ranchers about upcoming weather risks. He points to the fact that increasing evapotranspiration got missed leading up to the summer of 2017. “We realized that if we were looking carefully at reference ET, we might have seen it about a month earlier. What would people have done? They would have changed their calf purchases. They would have figured out what kind of forage they needed to buy. These are the types of decisions people can make if they know the information sooner.”

Was the drought over? Soil moisture illuminates the bigger picture

Heavy rains came mid-September of 2017, which led some people to believe the drought was over. However, changes in soil moisture told a different story. Very little of the rain made it into the soil. “At the Havre, MT station you can see we had some heavy precipitation events. Then we had early October snows. So people expected good soil water recharge. But at the end of the day, we didn’t get it. On Sept.15th, soil moisture sensors showed a big soil moisture response at the surface but only a marginal response at 8 inches.” The melt of early October snows onto the soil, still damp from the September rain, drained to 20 inches or more. But as the snowmelt dissipated, there was minimal net gain going into the winter.

Figure 2. Soil moisture traces at the Havre, MT weather station

Predictive models need more coverage to be effective

Typically in the U.S., the National Weather Service (a division of NOAA) puts out a network of weather monitoring stations spaced out across the country, and that data gets fed into forward-looking models that help predict the weather. Dr. Doug Cobos, research scientist at METER says, “What people are finding out is that putting in a sparse network of very expensive systems has done really well. It’s been a good thing. But the spatial gaps in those networks are a problem, especially for agriculture producers and ranchers. They need to know what’s happening where they are.”

Hyde agrees, adding that we need better predictive tools that help growers and ranchers make practical decisions based on data rather than guessing. “January 1st is when the decision has to be made—do I buy cows? Do I sell cows? Do I need more pasture? But many predictions start on April 1st. As one rancher puts it, ‘We don’t bother with Las Vegas. We sit around the dining room table at the beginning of the year and put a million dollars on one shot.’”

Mesonets improve spatial distribution

Mesonets present a practical solution for the need to fill in data gaps between large, complex weather stations. The Montana Mesonet currently has 57 stations interspersed throughout the state, and through partnerships with both the public and private sector, they’re adding more stations every year.

Figure 3. Map of MT Mesonet weather stations (source: http://climate.umt.edu/mesonet/)

At each location, the Montana Mesonet team installs METER all-in-one weather stations, soil moisture sensors, NDVI sensors and data loggers that integrate with ZENTRA Cloud: an easy-to-use web software that seamlessly integrates into third-party applications through an API. He says the system enables better spatial distribution and reliability. “When we were deciding on equipment we asked ourselves: What kind of technology should we use? It had to provide high data integrity. It had to be easy to deploy and maintain. And it had to be cost effective. There’s not a lot of people in that sector. METER systems are low profile, they’re affordable, and the reliability is there. I look at some other mesonets, and they cannot afford to build out further because they are relying on large, complex, expensive systems. That’s where the METER system comes into play.”

Figure 4. Montana Mesonet station setup (Photo credit: Kevin Hyde)

Betting on the future

The Mesonet team and its partners are excited to see how their data will mesh with the available predictive tools to be the most useful and practical for growers and ranchers throughout the state, and they realize that there is still much work to do. “It’s not enough just to get the instrumentation out there. The overall crux is: how do we build the information network, and how do we build a relationship with the producers so that we can have an iterative and interactive conversation?” says Hyde. “We know there needs to be an education in how to use and interpret the data. For example: what is NDVI, and what can we learn from it? A lot of what we need to do is translate science into practical terms.” But he adds that it doesn’t need to be perfect. “What the farmers have said to us is, ‘We don’t need exact numbers. We’re gamblers. Give us probability. Teach us what it means, and we’ll make the decision.’”

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Jan 11

Water holding and temperature patterns of canopy soil in an old-growth forest

The deadline is fast approaching to apply for the 2019 Grant A. Harris Fellowship. The fellowship awards $10,000 in METER research instrumentation to six U.S. or Canadian graduate students studying any aspect of agricultural, environmental, or geotechnical science.

Camila Tejo Haristoy using METER soil moisture and temperature sensors

(Image source: https://vimeo.com/69136931)

Camila Tejo Haristoy, former University of Washington grad student, was a Grant A. Harris Fellowship winner. She used METER soil moisture and temperature sensors to study the water holding and temperature patterns of canopy soil in an old-growth Sitka Spruce forest in Washington state. Sitka Spruce tree crowns contain large accumulations of organic matter known as “canopy soil”. These accumulations provide substrate and habitat for a broad community of plants, insects, and other arboreal species. Using tree-climbing techniques, Camila installed soil moisture sensors in the canopy soils of spruce trees from an old-growth stand in the Olympic Peninsula, Washington.

This study characterized for the first time environmental conditions associated with soil mats within the crown of spruce trees, providing a framework for understanding the distribution and activity of epiphytic plants, nutrient dynamics, and associated canopy organisms.

Watch the documentary

Watch a fascinating 7-minute documentary of Camila’s interesting and exciting research. The documentary description: “Camila spends long rainy days climbing into treetops, taking temperature and moisture measurements, and collecting soil and plant samples. In the process, she interacts with a seldom seen, barely understood, and lushly beautiful environment.” (source https://vimeo.com/69136931)

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Recharge your research

Apply for the Grant A. Harris Fellowship today.

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Sep 10

Data collection: 8 best practices to avoid costly surprises

Every researcher’s goal is to obtain usable field data for the entire duration of a study. A good data set is one a scientist can use to draw conclusions or learn something about the behavior of environmental factors in a particular application. However, as many researchers have painfully discovered, getting good data is not as simple as installing sensors, leaving them in the field, and returning to find an accurate record. Those who don’t plan ahead, check the data often, and troubleshoot regularly often come back to find unpleasant surprises such as unplugged data logger cables, soil moisture sensor cables damaged by rodents, or worse: that they don’t have enough data to interpret their results. Fortunately, most data collection mishaps are avoidable with quality equipment, some careful forethought, and a small amount of preparation.

Before selecting a site, scientists should clearly define their goals for gathering data.

Make no mistake, it will cost you

Below are some common mistakes people make when designing a study that cost them time and money and may prevent their data from being usable.

Site characterization: Not enough is known about the site, its variability, or other influential environmental factors that guide data interpretation
Sensor location: Sensors are installed in a location that doesn’t address the goals of the study (i.e., in soils, both the geographic location of the sensors and the location in the soil profile must be applicable to the research question)
Sensor installation: Sensors are not installed correctly, causing inaccurate readings
Data collection: Sensors and logger are not protected, and data are not checked regularly to maintain a continuous and accurate data record
Data dissemination: Data cannot be understood or replicated by other scientists

When designing a study, use the following best practices to simplify data collection and avoid oversights that keep data from being usable and ultimately, publishable.

IoT Technologies for Irrigation Water Management (Part 2)

Dr. Yossi Osroosh, Precision Ag Engineer in the Department of Biological Systems Engineering at Washington State University, continues (see part 1) to discuss the strengths and limitations of IoT technologies for irrigation water management.

Informed irrigation decisions require real-time data from networks of soil and weather sensors at desired resolution and at a reasonable cost.

LoRaWAN (a vendor-managed solution see part 1) is ideal for monitoring applications where sensors need to send data only a couple of times per day with very high battery life at a very low cost. Cellular IoT, on the other hand, works best for agricultural applications where sensors are required to send data more frequently and irrigation valves need to be turned on/off. Low-Power Wide-Area Networking (LPWAN) technologies need gateways or base stations for functioning. The gateway uploads data to a cloud server through traditional cellular networks like 4G. Symphony Link has an architecture very similar to LoRaWAN with higher degree of reliability appropriate for industrial applications. The power budget of LTE Cat-M1 9 (a network operator LPWAN) is 30% higher per bit than technologies like SigFox or LoRaWAN, which means more expensive batteries are required. Some IoT technologies like LoRa and SigFox only support uplink suited for monitoring while cellular IoT allows for both monitoring and control. LTE-M is a better option for agricultural weather and soil moisture sensor applications where more data usage is expected.

NB-IoT is more popular in EU and China and LTE Cat-M1 in the U.S. and Japan. T-Mobile is planning to deploy NB-IoT network in the U.S. by mid-2018 following a pilot project in Las Vegas. Verizon and AT&T launched LTE Cat-M1 networks last year and their IoT-specific data plans are available for purchase. Verizon and AT&T IoT networks cover a much greater area than LoRa or Sigfox. An IoT device can be connected to AT&T’s network for close to $1.00 per month, and to Verizon’s for as low as $2 per month for 1MB of data. A typical sensor message generally falls into 10-200 bytes range. With the overhead associated with protocols to send the data to the cloud, this may reach to 1KB. This can be used as a general guide to determine how much data to buy from a network operator.

Studies show there is a potential for over 50% water savings using sensor-based irrigation scheduling methods.

What the future holds

Many startup companies are currently focused on the software aspect of IoT, and their products lack sensor technology. The main problem they have is that developing good sensors is hard. Most of these companies will fail before the batteries of their sensors die. Few will survive or prevail in the very competitive IoT market. Larger companies that own sensor technologies are more concerned with the compatibility and interoperability of these IoT technologies and will be hesitant to adopt them until they have a clear picture. It is going to take time to see both IoT and accurate soil/plant sensors in one package in the market.

With the rapid growth of IoT in other areas, there will be an opportunity to evaluate different IoT technologies before adopting them in agriculture. As a company, you may be forced to choose specific IoT technology. Growers and consultants should not worry about what solution is employed to transfer data from their field to the cloud and to their computers or smartphones, as long as quality data is collected and costs and services are reasonable. Currently, some companies are using traditional cellular networks. It is highly likely that they will finally switch to cellular IoT like LTE Cat-M1. This, however, may potentially increase the costs in some designs due to the higher cost of cellular IoT data plans.

IoT Technologies Chart

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Jan 15

PRI & the Power of Spectral Indices

In this brief 30-minute webinar, Dr. John Gammon, University of Alberta, teaches the basics of the Photochemical Reflectance Index (PRI).

He gives an introduction to the photochemical reflectance index and what it can tell researchers about xanthophyll cycle activity, carotenoid: chlorophyll pigment ratios, light-use efficiency, and plant stress. He also discusses remote sensing.

Topics include:

Energy distribution in a leaf
Leaf optical changes upon shade removal
Photosynthetic light response curve
Uses as a stress indicator
Temporal and spacial patterns in photoprotection
How does photoprotection vary with tree age?
Kinetics: sun vs. shade
Applications
Can it “scale”?
Light-use efficiency model

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More canopy webinars:

Using PRI to Monitor Crop Stress

Leaf Area Index: Theory, Measurement, and Application

NDVI and PRI: Measurement, Theory, and Application

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Jan 2

Soil Moisture Sensors: Why TDR vs. Capacitance May Be Missing the Point

Researcher holding a soil sensor in front of a field

Soil moisture sensor

Time Domain Reflectometry (TDR) vs. capacitance is a common question for scientists who want to measure volumetric water content (VWC) of soil, but is it the right question? Dr. Colin S. Campbell, soil scientist, explains some of the history and technology behind TDR vs. capacitance and the most important questions scientists need to ask before investing in a sensor system. Read more…

Get More From your NDVI Sensor

Modern technology has made it possible to sample Normalized Difference Vegetation Index (NDVI) across a range of scales both in space and in time, from satellites sampling the entire earth’s surface to handheld small sensors that measure individual plants or even leaves. Read more…

Improved Methods Save Money in Future Borehole Thermal Energy Storage Design

Globally, the gap between the energy production and consumption is growing wider. To promote sustainability, University of California San Diego PhD candidate and ASCE GI Sustainability in Geotechnical Engineering committee member, Tugce Baser, Dr. John McCartney, Associate Professor, and their research team, Dr. Ning Lu, Professor at Colorado School of Mines and Dr. Yi Dong, Postdoctoral Researcher at Colorado School of Mines, are working on improving methods for borehole thermal energy storage (BTES), a system which stores solar heat in the soil during the summer months for reuse in homes during the winter. Read more…

New Weather Station Technology in Africa

Weather data, used for flight safety, disaster relief, crop and property insurance, and emergency services, contributes over $30 billion in direct value to U.S. consumers annually. Since the 1990’s in Africa, however, there’s been a consistent decline in the availability of weather observations. Read more…

Electrical Conductivity of Soil as a Predictor of Plant Response

Plants require nutrients to grow, and if we fail to supply the proper nutrients in the proper concentrations, plant function is affected. Fertilizer in too high concentration can also affect plant function, and sometimes is fatal. Read more…

And our three most popular blogs of all time:

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 co-authored with Dr. Marco Bittelli. Read more…

How to Measure Water Potential

In the conclusion of our three-part water potential series, we discuss how to measure water potential—different methods, their strengths, and their limitations. Read more…

Do the Standards for Field Capacity and Permanent Wilting Point Need to be Reexamined?

We were inspired by this Freakonomics podcast, which highlights the book, This Idea Must Die: Scientific Problems that are Blocking Progress, to come up with our own answers to the question: Which scientific ideas are ready for retirement? We asked scientist, Dr. Gaylon S. Campbell, which scientific idea he thinks impedes progress. Here’s what he had to say about the standards for field capacity and permanent wilting point. Read more…

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Dec 8

Irrigation Curves—A Novel Irrigation Scheduling Technique

This week, guest author Dr. Michael Forster, of Edaphic Scientific Pty Ltd & The University of Queensland, writes about new research using irrigation curves as a novel technique for irrigation scheduling.

Corn field with a blue cloudy sky background

Growers do not have the time or resources to investigate optimal hydration for their crop. Thus, a new, rapid assessment is needed.

Measuring the hydration level of plants is a significant challenge for growers. Hydration is directly quantified via plant water potential or indirectly inferred via soil water potential. However, there is no universal point of dehydration with species and crop varieties showing varying tolerance to dryness. What is tolerable to one plant can be detrimental to another. Therefore, growers will benefit from any simple and rapid technique that can determine the dehydration point of their crop.

New research by scientists at Edaphic Scientific, an Australian-based scientific instrumentation company, and the University of Queensland, Australia, has found a technique that can simply and rapidly determine when a plant requires irrigation. The technique builds on the strong correlation between transpiration and plant water potential that is found across all plant species. However, new research applied this knowledge into a technique that is simple, rapid, and cost-effective, for growers to implement.

Current textbook knowledge of plant dehydration

The classic textbook values of plant hydration are field capacity and permanent wilting point, defined as -33 kPa (1/3 Bar) and -1500 kPa (15 Bar) respectively. It is widely recognized that there are considerable limitations with these general values. For example, the dehydration point for many crops is significantly less than 15 Bar.

Furthermore, values are only available for a limited number of widely planted crops. New crop varieties are constantly developed, and these may have varying dehydration points. There are also many crops that have no, or limited, research into their optimal hydration level. Lastly, textbook values are generated following years of intensive scientific research. Growers do not have the time, or resources, to completely investigate optimal hydration for their crop. Therefore, a new technique that provides a rapid assessment is required.

How stomatal conductance varies with water potential

There is a strong correlation between stomatal conductance and plant water potential: as plant water potential becomes more negative, stomatal conductance decreases. Some species are sensitive and show a rapid decrease in stomatal conductance; other species exhibit a slower decrease.

Plant physiologist refer to P50 as a value that clearly defines a species’ tolerance to dehydration. One definition of P50 is the plant water potential value at which stomatal conductance is 50% of its maximum rate. P50 is also defined as the point at which hydraulic conductance is 50% of its maximum rate. Klein (2014) summarized the relationship between stomatal conductance and plant water potential for 70 plant species (Figure 1). Klein’s research found that there is not a single P50 for all species, rather there is a broad spectrum of P50 values (Figure 1).

Figure 1. The relationship between stomatal conductance and leaf water potential for 70 plant species. The dashed red lines indicate the P80 and P50 values. The irrigation refill point can be determined where the dashed red lines intersect with the data on the graph. Image has been adapted from Klein (2014), Figure 1b.

Taking advantage of P50

The strong, and universal, relationship between stomatal conductance and water potential is vital information for growers. A stomatal conductance versus water potential relationship can be quickly, and easily, established by any grower for their specific crop. However, as growers need to maintain optimum plant hydration levels for growth and yield, the P50 value should not be used as this is too dry. Rather, research has shown a more appropriate value is possibly the P80 value. That is, the water potential value at the point that stomatal conductance is 80% of its maximum.

Irrigation Curves – a rapid assessment of plant hydration

Research by Edaphic Scientific and University of Queensland has established a technique that can rapidly determine the P80 value for plants. This is called an “Irrigation Curve” which is the relationship between stomatal conductance and hydration that indicates an optimal hydration point for a specific species or variety.

Once P80 is known, this becomes the set point at which plant hydration should not go beyond. For example, a P80 for leaf water potential may be -250 kPa. Therefore, when a plant approaches, or reaches, -250 kPa, then irrigation should commence.

P80 is also strongly correlated with soil water potential and, even, soil volumetric water content. Soil water potential and/or content sensors are affordable, easy to install and maintain, and can connect to automated irrigation systems. Therefore, establishing an Irrigation Curve with soil hydration levels, rather than plant water potential, may be more practical for growers.

Example irrigation curves

Irrigation curves were created for a citrus (Citrus sinensis) and macadamia (Macadamia integrifolia). Approximately 1.5m tall saplings were grown in pots with a potting mixture substrate. Stomatal conductance was measured daily, between 11am and 12pm, with an SC-1 Leaf Porometer. Soil water potential was measured by combining data from an MPS-6 (now called TEROS 21) Matric Potential Sensor and WP4 Dewpoint Potentiometer. Soil water content was measured with a GS3 Water Content, Temperature and EC Sensor. Data from the GS3 and MPS-6 sensors were recorded continuously at 15-minute intervals on an Em50 Data Logger. When stomatal conductance was measured, soil water content and potential were noted. At the start of the measurement period, plants were watered beyond field capacity. No further irrigation was applied, and the plants were left to reach wilting point over subsequent days.

Figure 2. Irrigation Curves for citrus and macadamia based on soil water potential measurements. The dashed red line indicates P80 value for citrus (-386 kPa) and macadamia (-58 kPa).

Figure 2 displays the soil water potential Irrigation Curves, with a fitted regression line, for citrus and macadamia. The P80 values are highlighted in Figure 2 by a dashed red line. P80 was -386 kPa and -58 kPa for citrus and macadamia, respectively. Figure 3 shows the results for the soil water content Irrigation Curves where P80 was 13.2 % and 21.7 % for citrus and macadamia, respectively.

Figure 3. Irrigation Curves for citrus and macadamia based on soil volumetric water content measurements. The dashed red line indicates P80 value for citrus (13.2 %) and macadamia (21.7 %).

From these results, a grower should consider maintaining soil moisture (i.e. hydration) above these values as they can be considered the refill points for irrigation scheduling.

Further research is required

Preliminary research has shown that an Irrigation Curve can be successfully established for any plant species with soil water content and water potential sensors. Ongoing research is currently determining the variability of generating an Irrigation Curve with soil water potential or content. Other ongoing research includes determining the effect of using a P80 value on growth and yield versus other methods of establishing a refill point. At this stage, it is unclear whether there is a single P80 value for the entire growing season, or whether P80 shifts depending on growth or fruiting stage. Further research is also required to determine how P80 affects plants during extreme weather events such as heatwaves. Other ideas are also being investigated.

For more information on Irrigation Curves, or to become involved, please contact Dr. Michael Forster: [email protected]

Reference

Klein, T. (2014). The variability of stomatal sensitivity to leaf water potential across tree species indicates a continuum between isohydric and anisohydric behaviours. Functional Ecology, 28, 1313-1320. doi: 10.1111/1365-2435.12289

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Oct 23

Apply now for the 2018 Grant A. Harris Fellowship

University of Idaho graduate student and past Grant A. Harris Fellowship recipient, Adrianne Zuckerman, is taking a different approach to stream restoration than the traditional approach, channel manipulation, which often requires heavy equipment and major disruption to the riparian area.

Zuckerman set out to understand how vegetation lining the stream bank impacts habitat quality for anadromous salmon and steelhead in Washington’s Methow River, which flows through the eastern Cascades. Zuckerman wanted to know how tree species composition affects the amount of nutrients available to the benthic insect community, since they are a critical food source for young salmonid fish.

When Zuckerman began investigating methods for measuring leaf contribution to the stream, she found that leaf litter traps were the standard equipment. Leaf litter traps are time-consuming to set and maintain, and data analysis consists of frequent visits to the field followed by extensive time in the lab processing leaf material.

Looking for an alternative method, she discovered the LP-80 ceptometer: a lightweight, field-portable instrument for measuring leaf area index (LAI). Using the LP-80, Zuckerman was able to rapidly assess the leaf area contribution of each tree species along the riparian corridor. Using this information, it was relatively straightforward for her to estimate the contribution of each tree species to the stream food web.

Zuckerman’s research will help land managers and other researchers understand the importance of riparian vegetation for maximizing the food available to salmonid fish species. Improvement and maintenance of optimal stream-side vegetation composition should ultimately help to enhance salmon populations in the Pacific Northwest.

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The Grant A. Harris Fellowship awards $40,000 in research instrumentation (four $10,000 awards) annually to graduate students studying any aspect of agricultural, environmental, or geotechnical science. METER is now accepting applications for the 2018 award. Learn more about how to apply for the Grant A. Harris Fellowship here.

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Aug 28

How to Assess Maximum Potential Biomass Production—Simplified

The conversion of light energy and atmospheric carbon dioxide to plant biomass is fundamentally important to both agricultural and natural ecosystems.

Potato field

The detailed biophysical and biochemical processes by which this occurs are well understood. At a less-detailed level, however, it is often useful to have a simple model that can be used to understand and analyze parts of an ecosystem. Such a model has been provided by Monteith (1977). He observed that when biomass accumulation by a plant community is plotted as a function of the accumulated solar radiation intercepted by the community, the result is a straight line. Figure 1 shows Monteith’s results.

Total dry matter produced by a crop as a function of total intercepted radiation in a diagram

Figure 1. Total dry matter produced by a crop as a function of total intercepted radiation (from Monteith, 1977).

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