Roots, Shoots, and Sky-High Science and Extension: Our dedicated team has actively engaged in research and extension events this year that offer valuable insights into plant ecology and climate change adaptation.
Field Research: Graduate student Scout Dahms-May led extensive research into how ornamental shrubs respond to drought conditions. Her dedication shone through as she ventured into the field for pre-dawn plant water potential assessments, sharing the experience with hot air balloonists and the local coyotes. Our excellent undergraduate students, along with the new graduate student, Josh Perrault, played a pivotal role in the research by meticulously measuring the leaf area of over 100 plants. Their hard work serves as a testament to the commitment of students pursuing cutting-edge agricultural research.
Extension: Standout events this season included an impressive demonstration of sprayer drones. Visitors had the opportunity to witness these cutting-edge technologies in action, gaining insights into how they can be used in modern agriculture and horticulture.
Another highlight was a grand field day that showcased the spirit of collaboration at NWREC, involving students, staff like Brent Warneke, Dalyn McCauley, and Clint Taylor from the Nackley Lab, as well as guest appearances by experts, including Dr. Rebelo, a visiting scholar from South Africa, and Dr. Wiman, Orchards Program Leader, and Dr. Yang, a Blueberry Extension Specialist. This summer, NWREC demonstrated its position as a hub of research, learning, and community engagement, driven by our shared commitment to advancing the field of plant science.
Kym Pokorny published this fantastic write up on the goings-on for the Climate Ready ornamental plant study we’ve been working on for the last few years – check it out here or click below the image to read more!
Unlocking Nature’s Water Secrets for Greener Futures, Part 1
TL;DR Plant hydraulics unravels the journey of water within plants, aiding tree health, nursery production, urban forest management, and climate resilience. 🌿🌿
Last month, we delved into the fascinating world of soil hydraulics, exploring how water moves beneath our feet. In this post, we’re staying within the realm of water movement but shifting our focus to a different dimension of nature – plants. Prepare to journey through the intricate pathways of plant hydraulic physiology, where we uncover the secrets of how trees and other woody plants manage water, adapt to challenging conditions, and ultimately contribute to a greener, more sustainable world.
Plant hydraulic physiology is all about how water moves through plants. Scientists study this to understand how trees and other woody plants react when they have enough water or not enough. This knowledge helps us figure out how different ways of growing plants in nurseries affects their growth. People have known for a while that this field is important for plants in forests. But now, thanks to recent discoveries by this lab and others, this amazing field of science is being applied to nurseries and other horticultural production systems. In this summary, I will explain the basic ideas about how water moves through plants , how it connects to their structure and how they work. With this knowledge, scientists, nursery workers, and people who care for forests can ensure they grow strong, healthy trees that can handle harsh conditions when planted outside.
UNDERSTANDING WATER MOVEMENT IN PLANTS Let’s start by talking about how water moves in plants. Imagine it’s like water moving through a hose in your garden. We can measure this flow of water using something called “flow rate,” which is just how much water moves in a certain amount of time.
We use units like gallons per minute or liters per minute to measure it. For example, think about a water hose in your garden. If you want to know how much water it sprays out in a minute, that’s its flow rate. Now, here’s something interesting: the size of the pipe or hose matters. A big hose can let a lot more water flow through than a tiny one. In fact if you double the diameter of a hose it can allow 4 times the flow of the smaller diameter hose. Plants have tiny water pipes called “xylem.”
XYLEM CONDUCTANCE Okay, now let’s talk about “conductance.” Think of it as how easy or hard it is for water to move through something. For plants, this refers to how easily water can travel through their pipes. We usually keep the pressure the same, like when you use a hose with a constant water pressure. This helps make sure the plants get water evenly. Lastly, there’s something called “conductivity.” It’s like a fancy version of conductance but scaled to the size of different parts of the plant. It helps us compare how different parts of the plant move water. For example, we might want to know how water moves through the stem compared to the roots.
Now, here’s where it gets cool: in plants, water doesn’t get pushed like in your garden hose. It gets pulled up by something called “tension.” This happens because plants lose water from their leaves when it evaporates. Imagine a plant sipping water through a straw from the soil. When the water evaporates from the leaves, it creates tension, like a vacuum pulling water up the plant. This is how water can move up the tallest trees. So, we measure something called “water potential” to understand this tension. It tells us how much “pull” the plant has on the water. When there’s a difference in water potential between different parts of the plant, it’s like a driving force that makes water move from where there’s less pull to where there’s more. This helps water move up from the roots to the leaves, even against gravity. We call this whole process the “Soil-Plant-Atmosphere Continuum,” but you can just think of it as how plants drink water.
And that’s the basics of how water moves in plants!
The Gravel Pad update you’ve been waiting for, and more!
There’s so much going on in the season of plenty around NWREC! Enjoy this virtual tour of a few projects around the nursery.
Dalyn has been continuing her work with mini-lysimeters that control irrigation in shade trees – these tiny scales weigh the potted plants and use the change in weight as they dry to determine when to turn on the water. The lysimeters are gathering data on plant weight along with an on-site weather station to better understand the relationship between heat and irrigation in gravel pad production. Read more about this project here.
The Willamette Valley has had a few HOT summers in a row, even though lately this one has been pretty mild. Nevertheless, we haven’t given up on finding solutions for heat mitigation – including growing ornamentals under drought conditions to see which are the most “climate-ready” to meet changing needs. We’ll be asking the public to evaluate those plants in the upcoming Climate-Ready Field Day, come along and see how the plants are progressing (click the link above for more info).
In addition, we’re evaluating different means of mitigating the heat and the resultant high rates of evapotranspiration (basically ways to reduce plant sweat), from misting the young plants to covering tissues with kaolin, introducing fungicides that may be beneficial in managing water loss, using white pots instead of the traditional black, and even growth inhibitors – it’s been a pretty amazing feat to monitor the effects as you can see- check out this monitoring station!
A small project growing marigolds for festivals and holidays – like Dia de los Muertos – is also underway. Growing the marigolds has certainly brightened up the Nursery Zone at NWREC, and we’ve progressed into evaluating passive means to dry the flowers, saving energy and resources while preserving the gorgeous summer color.
There’s even more in the works – stay tuned for information about fall workshops and PACE courses created specifically for nursery and greenhouse production for topics covering drone sprays, integrated pest management, and more.
At the Western Region International Plant Propagators Society (IPPS), the Pacific Northwest Insect Management Conference (PNWIMC), and the Orchard Pest and Disease Management Conference (OPDMC) last month, we presented cutting-edge research and advancements in our field. Our presentations at the Western Region IPPS and PNWIMC focused on the latest developments in sensor-controlled irrigation, and flatheaded borer management, respectively.
At the Orchard Pest and Disease Management Conference, we discussed the latest techniques in IPM for managing powdery mildew with biological fungicides applied by our laser-guided Intelligent Sprayer system. Through our presentations at these conferences, we aim to advance the knowledge and understanding of plant health in our field and to promote collaboration among professionals. By sharing our research and engaging in discussions with our peers, we strive to advance the science of horticultural production to support the growth and success of the horticulture in the Pacific Northwest region.
At NWREC, we have been working on our new hydroponic greenhouse project. However, since October we have encountered construction challenges in connecting the natural gas heaters, which has impacted the growth of crops such as lettuce, tomatoes, and cucumbers. As a result, lettuce growth has been slow and plagued by Botrytis, and warmer-growing crops like tomatoes and cucumbers have fared even worse. We are working to resolve the permitting issues with the heaters as soon as possible and look forward to updating you on the progress of the greenhouse project in the coming year.
For the past few years we’ve limited gatherings on the farm due to COVID-19 restrictions. In the summer of 2022, however, we were finally able to welcome the public back for Nursery Program Field Days. We’d like to take this opportunity to boast about a few of our highlights from the last several months.
For the first time, the Nackley Nursery Production team was an official stop on the Oregon Association of Nurseries Farwest Innovative Production Grower Tour. Our portion of the tour at NWREC showcased sensor-controlled irrigation, heat-stress mitigation techniques, LiDAR smart-sprayer systems, and practices that can reduce boxwood blight spread, and methods of scouting and monitoring insects in nurseries and greenhouses. These projects offer a wide range of savings for growers.: up to 80% improvement in irrigation efficiency, up to 70% reduction in sprayed pesticides, and a significant reduction in boxwood blight infection.
The second big event was an open house for our Climate Ready Landscape Plant trial, the largest coordinated landscape plant irrigation trial in the Western US. Plant professionals from around the region came to rate plants and discuss how we, as a society, are going to maintain healthy landscapes while faced with increasing extreme weather.
Ongoing projects that will continue this year include, research by our graduate student Sadie Keller, who is investigating Oak and Maple drought tolerance. This summer, Sadie shared her preliminary findings with scientists at the American Society for Horticultural Science, in Chicago.
In addition, Dr. Melissa Scherr continues our research on the Pacific Flatheaded beetle, with the anticipation of a grower event hosted at NWREC discussing current research on Flathead Borer biology and control this coming April – 2023.
The tour route will travel through fields with uneven terrain. Farm cart transport (e.g. gators) can be available for those who request assistance.
Schedule of Events
Field Tour 11 :00 -11:15 Station 1. Welcome, overview of the program and biostimulant research on Shade-Trees 11:15 – 11:30 Station 2. Plant-based irrigation scheduling: pressure bomb and infra-red thermography 11:30 – 11:45 Station 3. ET-based irrigation scheduling and Flatheaded borer research 11:45 – 12:00 Station 4. Cover cropping and Heat-stress prevention 12:00 – 12:15 Station 5. Boxwood blight control 12:15 – 12:30 Station 6. LiDAR “smart” air-blast sprayer and drone demonstration
12:30 – 1:00 Station 1. Open chat with research team, refreshments and grilled sides.
Open House 1:00 – 2:00 Self guided tour. Researchers will be at each of the six stations to answer questions. Sprayer demos will take place at station 6 every 15 mins.
Shade tree growers need to be prepared for the effects of climate change in Oregon.
In order to equip growers with the tools necessary for production success, we aim to determine critical shade tree stress thresholds, characterize plant responses to drought conditions, and correlate remotely collected spectral images with ground based plant water stress measurements.
Previous studies have sought drought response measurements for Acer rubrum (Red Maple) and Quercus rubra (Red Oak), but never in a nursery production setting.
We aim to disseminate this information to Oregon shade tree growers at the completion of this experiment with the hope to aid growers in making data driven irrigation decisions and demonstrate the use of these technologies in nursery production settings.
In Oregon’s Willamette Valley, the heart of the nursery country, rainfall is scarce during the summer and humidity is low. Oregon’s dry summer conditions can lead to low moisture stress conditions for maples and oaks in normal years. Plant stress resulting from low soil moisture, high heat, and low relative humidity have been exacerbated in recent years with the increasing frequency of heatwaves and drought. Drought and heat stress scorch the maple and oak canopies, which can lead to decreased plant quality and economic losses for shade tree growers. Sensor-based technologies can be used to model plant responses to environmental gradients to develop warning systems to help growers prevent stress and bridge a knowledge gap in the nursery production industry regarding drought responses.
How are we studying plant stress responses?
Starting late June 2022, we will implement two irrigation treatments (well-watered and drought) in our shade tree planting with each row having independent irrigation control. The well-watered rows will be maintained at a soil water potential of >-1.0 mPa. The drought treatment rows will be allowed to naturally dry down to a soil water potential of -4 mPa. If during the experiment, our metrics (stomatal conductance and stem water potential) do not show considerable responses at -4 mPa tension, we will allow the drought treatment to continue to dry down progressively (-1 mPa) until stress is evident.
Why and how do we measure stem water potential?
Plant water status is commonly defined in terms of water potential or the ability of the water to do work. In most cases, well watered plants have “high” water status and drought conditions lead to a “low” water status (Levin and Nackley 2021). Using the pressure chamber, we will take midday stem water potential measurements twice weekly from 12pm-3pm. This time frame is important because it represents the time of day where leaf transpiration is at its maximum.
First, we will cover the leaf and stems to be measured with an opaque bag for at least 10 minutes before pressurization to allow the plant to stop transpiring. Once we excise the sample from the tree it should be placed into the pressure chamber or “pressure bomb” within 30 seconds (Levin 2019). Once the stem is placed into the chamber and pressure is applied, the amount of pressure that it takes to cause water to appear at the cut surface tells us how much tension the stem is experiencing.
Why and how do we measure stomatal conductance?
We measure stomatal conductance using a porometer that measures the degree of stomatal openness and the number of stomata (Licor.com). This indicates the plant’s physiological response to its current environment. If a plant is stressed, it will tend to close its stomata and lower the stomatal conductance rate. We will be using a combination of the LI-6800 Portable Photosynthesis System and the LI-600 Porometer/Fluorometer to make our measurements twice a week from 12pm-3pm.
For more information:
Please stay tuned in the coming months for more blog posts about how we will find plant stress thresholds by measuring the hydraulic conductivity of these shade trees. We will also correlate remotely collected spectral and thermal images with our ground based plant stress measurements to demonstrate how implementing a UAS equipped with a multispectral and thermal camera can be used to detect water stress in nursery production.
I grew up in a small rural town in East Texas, deep behind the piney wood curtain in a land dominated by giant loblolly pines, muddy windy rivers, and air so thick and humid it felt like you were wearing it. When was a teenager I mowed lawns and fixed up garden beds. One client I had, Miss Trixie, was getting on up in her years. She had an amazing green thumb but her age had was limiting her mobility. She would coach me through everything I did – pulling weeds, planting annuals, pruning, and fertilizing. She left me with a love of horticulture that I will carry until the end of my days.
I enriched that love by getting a BS in Horticulture at Texas A&M. While I was there I worked as a student worker for a rose and peach breeder. It was where I first learned about the land grant system and the mission of extension, and I thought at the time that is sounded like a really fun job. I also met my wife through that job. She was a horticulture student as well, and she worked on the roses and I worked on the peaches. We just never stopped hanging out, now we have been married for almost 10 years.
After I graduated from Texas A&M I enrolled in a Masters International program at Oklahoma State University. The program merges graduate school and serving in the United States Peace Corps into one. After a little over a year of studies at OSU my wife and I were sent to Panama to serve as volunteers in an indigenous community deep in the rain forest near the Columbian border. My time in the Peace Corps was good, but also very challenging. We lived in one of the most remote sites of any of Peace Corps Volunteer in the world at that time. Illness and isolation were persistent challenges, but it was very rewarding work. We taught home gardening, and worked on clean water projects. When we left many folks in our little village of 100 people were growing their own veggies for the first time.
When we returned from Panama, I took a job for a year working for Texas A&M Extension and Research doing an irrigation trial on dent corn in the high desert of Arizona. I lived and worked on a couple 1000 acre farm and learned a great deal about irrigation. A family illness brought us back to East Texas, and we became teachers. We taught high school biology and environmental science for 5 years. We used our summer breaks and holidays to build a house. Little by little we built the whole thing ourselves in cash over 4 years. After resting for 1 year we decided that we were tired of living in such a hot and humid place and decided to pack up and move “somewhere you can see mountains”. In June of 2019 I got a job working for the Small Farms Program here at NWREC and we moved to the great Pacific Northwest and never looked back.
Living and working in the Willamette valley is such rewarding experience. It is truly a horticultural paradise, with some world class soils and growers. I get do something a little different every day, sometimes installing research trials or putting together workshops for growers, and there are always endless opportunities to hone my horticultural skills.
Nurseries grow a wide variety of species and use many different crop production methods which can make effectively scheduling irrigation difficult.
Mini-lysimeters are devices that measure evapotranspiration (ET) via a change in weight of a containerized crop.
Mini-lysimeter controlled irrigation has shown to reduce water use and conserve nutrients while producing plants of marketable size and quality.
The need for sensor-controlled irrigation
Irrigation scheduling for nursery is complex due to the wide variety of species grown, the variety of pot sizes, the differences in growing media, and differences in environmental conditions (i.e. greenhouses, hoop-houses, field nurseries, or use of shade cloths). These factors all influence the specific crop water requirements, making it difficult to determine a generalized irrigation solution. As such, irrigation scheduling is commonly based on grower intuition and experience. For example, it is common for an experienced grower to pick up pots as they walk through a can-yardto get a feel for the weight and irrigation need. With funding support from the ODA-OAN research program, we sought out to develop an automated sensor-controlled irrigation system that is based off container weight, referred to as a mini-lysimeter controlled irrigation system.
What are lysimeters?
Lysimeters are devices that directly measure crop evapotranspiration (ET), which is the transfer of water from the soil to the atmosphere through plants by transpiration, and from the soil by evaporation. Lysimeters consist of a tank filled with soil and crop that is placed on a scale. Any change in weight of the tank is a direct measure of water moving in or out of the system. This provides a direct measurement of water consumption from the tank’s boundary, which can be used to inform irrigation scheduling. Lysimeters have historically been used in agronomic crops like wheat, alfalfa, or legumes. However, they can be scaled down for use in nursery and greenhouse crops, which are often referred to as mini-lysimeters (Fig. 1). You can read more about mini-lysimeters and their many applications in our recent publication.
System Design The mini-lysimeter controlled irrigation system at the NWREC consists of 16 mini-lysimeters. They are suitable for measuring up to 10kg (22 lbs.), which can accommodate up to a 3-gal container (Fig. 2). The mini-lysimeters are hooked up to a Campbell Scientific CR1000X data logger (Campbell Scientific Inc, Logan, UT) using a multiplexer. The system is programmed to trigger irrigation for a zone based on the average container weight. This ensures that the applied irrigation is representative of the variability between containers, such as differences in the water holding capacity of the media, and irrigation uniformity. A guide detailing the design, calibration, and performance of the mini-lysimeter controlled irrigation system and can be found here.
System Performance When mini-lysimeter controlled irrigation is compared to traditional irrigation methods (i.e. irrigation on a timer), it has shown to use less water while producing plants of equal size and quality. Read more about this study here. Mini-lysimeter-controlled irrigation also responds more effectively to the seasonal and daily variations in water demand, increasing irrigation frequency during hot and dry conditions, and foregoing irrigation during cooler days or after rain. This is particularly salient as extreme weather events become more frequent. Having another set of eyes (sensors) looking over your crops can help reduce losses from over- and under-watering.