Sensor-controlled sprayers for specialty crop production

NEW PUBLICATION!

Recently our own Brent Warneke wrote another great article for Sprayers 101 covering the Intelligent Sprayer System – check it out here: https://sprayers101.com/airblast-sensors/

Want a preview? Here’s a synopsis:

Air-blast sprayers are versatile, reliable, and can be modified to fit numerous types of crops, all of which are reasons for their continued popularity. Yet despite their popularity, air-blast sprayers have long had a reputation for inefficient application characteristics. Sensor controlled spray systems reduce labor costs and pesticide waste. Recently, they are receiving renewed interest as their reliability has improved and more options have become available. There are two main types of sensor sprayers:

+ On/off sensor sprayers
+ Crop adapting sprayers

 A classic low-profile axial airblast sprayer.
 A classic low-profile axial airblast sprayer.

Sensor types
Infrared sensors: The inability to resolve characteristics of plant structure makes IR sensors suited to less complex applications such as triggering
the sprayer on and off at a plant. Additionally, these systems can be used for herbicide sprayers where the sensors are aimed at the trunks of trees/vines and turn off the sprayer as they pass the trunk or to target it for the purpose of sucker sprays.

Ultrasonic sensors: using multiple sensors, it’s possible to collect canopy volume data with similar accuracy to taking manual measurements. These are typically used on canopy sprayers with around 3 sensors per side of the sprayer.

Laser sensors (LiDAR): Provides the most accurate measurements of plant structure (mm resolution). Only one sensor needed for accurate measurement.

Plant fluorescence sensors: These have a spatial resolution between ultrasonic sensors and LiDAR sensors. Most commonly used on “weed-seeing” herbicide sprayers but also on canopy sprayers. All sensor sprayers must have a speed sensor to synch the sprayer ground speed to the sensor system.

Spraying with sensor sprayers
Insect pest and disease control with sensor controlled sprayers has
been widely shown to be similar to that of standard sprayers. Control can be achieved on those crops with spray volume savings from 20-70% depending on the sensor system used and crop spray volume savings are higher in crops with more variability labor savings, less pesticide release into the environment, tractor wear, and driver fatigue are also reduced as the sprayer is in operation for less time.

Sensor sprayers can result in 20% to over 90% less spray drift. Autonomous sensor sprayers companies are currently developing and selling autonomous sprayer units that drive themselves and can be integrated with sensors.

Illustration of on/off sensor sprayers (A) and canopy adapting sensor sprayers (B). Sensors are illustrated with red ovals and sensor field of view illustrated with grey shaded washes.

Meet the Team: The Bounty of a Season

Success in Summer 2022

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.

Sadie Keller presenting to growers
Sadie Keller discusses shade tree physiology

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.

image shows participants examining landscape plants
Stakeholders evaluating climate-readiness of various landscape ornamentals

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.

Sadie Keller and Lloyd Nackley at the ASHS Meeting 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 Nursery Program Team, summer 2022.

People: From Hiking to Horticulture

Scout Dahms-May

I am originally from the great city of Tacoma, Washington. I went to an outdoors based high school where my love for plants and environmentalism blossomed. My favorite class was our version of “PE”, where we hiked through Point Defiance Park identifying native species. This passion drove me to pursue a bachelor’s degree in Environmental Science at the University of Redlands. Moving to Redlands in Southern California was a stark contrast to my home in Puget Sound, but I grew to love most parts of it!

Scout collecting samples
Scout collects samples

I went on many abroad terms and saw amazing parts of the world such as Peru, Ethiopia, and Iceland. Each time I returned I wished I had been there longer and itched to immerse myself even more in a different country.  Once I graduated from Redlands, the natural next step was to join the Peace Corps. I spent two years in the Southeast corner of Senegal, West Africa. I lived in a 100-person village in the region of Kedougou where I learned to speak Jaxanke. As an Agroforestry Extension Agent, I helped with various agriculture and agroforestry projects.  We created small-scale nurseries, collected seeds, showcased new and improved agroforestry techniques, and outplanted trees and shrubs around the village. I loved my time in Senegal and miss being there constantly.

After returning to the United States, I moved to Eugene, OR to work at Dorena Genetic Resource Center. I assisted the lead horticulturist in end-to-end native plant restoration, collecting/processing seed, and producing native plants to restore areas affected by fires, floods, and construction. I became the lead irrigator, which was a new problem-solving and damp adventure, and led seed collection trips across Oregon. I also helped develop a seed collection mapping application to track plant populations and store seed collection data.

This leads me to OSU! I just started at OSU this fall to pursue my Masters in Horticulture and work in the Nackley Lab. I am partnered with Sadie Keller on a project looking at stem hydraulics and how it relates to drought in shade trees. I am new to this type of research but am so eager to learn more! I am excited to get our stem hydraulics lab up and running and start the journey of data collection.

Climate-Ready Landscape Plant FIELD DAY

UC Davis Plant Trial Field Day 2020
Photos: UC Davis Plant Trial Field Day 2020 cr: Karrie Reid

Who should attend: Professionals from landscape, horticulture, nursery and related fields; OSU Master Gardeners; garden writers; academics/educators

When: September 14th 2022; 10am – 2pm (Arrive when convenient; ratings take about 60 min)

Where:                  OSU’s North Willamette Research & Extension Center

15210 NE Miley Rd, Aurora, OR 97002

What’s involved: Evaluating aesthetic qualities of selected landscape plants (about 60 minutes).

Photos: UC Davis Plant Trial Field Day 2020 Credit: Karrie Reid
Photos: UC Davis Plant Trial Field Day 2020 Credit: Karrie Reid

About this Event

The ever-changing climate iputs pressure on the industry to develop more sustainable plants. As part of a six-university study, OSU seeks to improve urban water-use efficiency by evaluating landscape plant performance on three irrigation treatments corresponding to the Water Use Classification of Landscape Species (WUCOLS): High, Moderate, and Low categories of water need. The plants are irrigated regularly during their first summer after planting. Treatments are imposed during the second growing season where researchers collect growth and quality ratings.

The Field Day allows landscape, nursery, and horticultural industry professionals and educators the opportunity to see new plants in their 2nd year and share your opinions and preferences by rating a representative sample of the plants in the field undergoing irrigation treatments. One plant from each of the 3 water levels, for 15 different species (some released to the public and some not yet) will be surveyed. Along with this field of 360 plants, you will be able to get a sneak peek at the next year’s field, currently in an establishment phase.

Important Details: The fields are packed dirt/uneven mulch, sturdy comfortable shoes, sunscreen and/or a hat are suggested. At the trial site, you will be provided a ratings sheet, clipboard, pen, and given general instructions when you arrive. It is a self-guided tour among our 720 landscape plants. Lots to look at but only a small sub set to evaluate. Hot Coffee and cold water will be provided. We value your feedback and hope to see you there!

For questions contact:

Brian Hill

(562) 841-1522

brian.hill@oregonstate.edu

2022 Field Day Tour and Open House

August 23, 2022

Nackley Lab nursery production open house takes place August 23. 2023 from 11am – 2pm

Our event will be a part of the great Nursery related activities happening around the Willamette Valley as part of the Oregon Association of Nurseries Farwest Show, which will also feature Dr. Nackley, and Brian Hill, M.S. and many others from Oregon State and beyond.

The Nackley lab open house will feature research on our four themes: Irrigation science, pest management, plant health, and plant trials.

Free to all, no registration required.

Parking: follow signs to south side of the Cravo North Willamette Research and Extension Center and then follow signs walk 5 mins (west) to Nackley Lab Welcome Center.


Masks are welcome, not required, per University policy

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.

People: Oregon bound and down; From the land of sun to the land of clouds

Brent Warneke

Brent inside the west cave of Monkey Face, Smith Rock State Park.

I grew up in Littleton, Colorado amid the suburbs of Denver. Although I was a suburb kid, I grew up gardening from an early age, which sparked my love for plants. Going with what I was interested in, I decided to pursue a degree in something plant related at Colorado State University. I ended up studying horticulture, but took a wide range of classes including brewing technology, microbiology, biochemistry and business. Throughout my time at CSU I worked in a couple different lab groups, one that studied biofuel production and another that was focused on cryopreservation of vegetatively propagated crops. Working in the labs got me interested in science. I took a plant pathology course my senior year and loved how it was an integration of things I had learned in horticulture, microbiology, and other sciences.

Eventually I obtained my BS in Horticultural Science and a minor in Business Administration at CSU. I had such a good time learning about science and working in labs that I decided to pursue graduate school. I looked at a few universities throughout the USA but the prospect of working on specialty crops (fruits and nuts) had me more excited than working on field crops. I ended up landing at Oregon State University in the Botany and Plant Pathology Department. The project I worked on had me investigating fungicide resistance and grape powdery mildew management and I was fortunate to travel to many vineyards throughout the state to take samples and work with growers. Over the course of my Master’s degree I was able to present data from my research at two national plant pathology conferences, one in Tampa, FL and the other in San Antonio, TX, two places I had never been before. These experiences were very useful to hone my science communication skills which I use a lot in my current position.

Brent at Glacier Lake while backpacking in the Eagle Cap wilderness.

After I finished my MS degree I started my current position working on the Intelligent Sprayer project at OSU with Drs. Lloyd Nackley and Jay Pscheidt. The part of the project I fit into investigates using the Intelligent Sprayer to manage grape powdery mildew with various fungicide regimes and investigating sprayer coverage in hazelnut and nursery crops. This has been a great fit for me as I have been able to apply what I learned during my MS and strengthen my research and writing skills. As with all agriculture, we come up with a plan every year and have ideas about how everything will go, but something always surprises us. During the season it’s always a push to collect all the data we need, but when the season is over it is very interesting to sit down, go through the data, and make graphs and connections as to how the treatments we applied fared. Writing up the data into informative reports, and in doing so, making connections to past literature while abstracting it into the future is another part of the process that makes me love what I do.

The 50 gallon air-blast sprayer retrofitted with the Intelligent Spray System connected to a Kubota M5-111 tractor that powers the unit.

I’ve been fortunate to live in two different states that are great for my outdoor oriented lifestyle. I grew up camping, fishing, backpacking, canoeing and skiing in Colorado. I have since gotten into rock climbing, rafting and kayaking, and hunting in Oregon, and especially love spending time on the Oregon coast. If I were to give some advice to someone following a similar career path to me I would tell them to always be open to opportunities and to get out of their comfort zone regularly.

Irrigation: Drought Physiology of Ornamental Shade Trees

Sadie Keller

Highlights:

  1. Shade tree growers need to be prepared for the effects of climate change in Oregon.
  2. 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.
  3. Previous studies have sought drought response measurements for Acer rubrum (Red Maple) and Quercus rubra (Red Oak), but never in a nursery production setting.
  4. 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.
Sadie in some of the shade trees equipped with soil moisture sensors and a weather station.
Sadie Keller in the shade trees equipped with soil moisture sensors and a weather station.

The Problem:

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.

The pressure chamber
The pressure chamber (https://www.pmsinstrument.com/)

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.

People: Amidst the Loblolly Pines

Clint Taylor

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.

couple backpacking in the mountains
Clint and his wife backpacking in the mountains

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.

Clint working on a mechanical pump
Setting up an irrigation pump in Panama for clean water projects

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.

Pest Management: Intelligent Sprayer system automatically adjusts to seasonal growth saving thousands of dollars per year

Lloyd Nackley

Highlights

  • Airblast sprayers should be calibrated throughout the growing season to maximize application efficiency.
  • The LiDAR guided Intelligent Sprayer system automatically adjusts to crop canopy sizes.
  • Compared to standard Airblast sprayers, the Intelligent Sprayer system can reduce pesticide volumes by more than 50% while achieving adequate coverage, reducing drift by > 33%.

Our research revealed  that the majority of directed canopy spraying of specialty crops (defined here as fruits, nuts, and horticultural crops) relies on the radial air blast sprayers. There are many reasons for the continued popularity of air blast sprayers such as customizable sizes, easily available parts for repairs, and robust construction using materials such as stainless steel that provide years of low maintenance use. Although the air blast sprayer continues to be an important and effective tool for the specialty crop industry, its widespread use has not been without issues.

When radial air blast sprayers were first popularized in the 1950s, standard production practices favored hand labor, tree varieties popular at the time were around 6 m tall at maturity, and vines had large dense canopies. Modern plant breeding and horticultural practices, such as pruning and training systems, have revolutionized specialty crop production leading to higher density production systems designed for mechanization. Modern horticulture favors smaller trees (1–4 m tall) that are more productive per unit area than their historical counterparts, and pruning and trellis systems that create more open canopies. Despite the physical transformation of specialty crop production systems, the design of radial air blast sprayers has stayed largely the same. Consequently, unmodified radial air blast sprayers emit air and pesticide volumes that are often much greater than needed in modern high-density, open canopy systems.

Air blast sprayers from their early years to current day. (A) ‘Speed Sprayer’ on the Brown Fruit Farm near Worthington, OH, USA, 1947 (image courtesy of worthingtonmemory.org). (B) Air blast sprayer being used in research trials at the Ohio Agricultural Research and Development Center, Wooster, OH, USA, 1966. (C) Air blast sprayer at Rears Manufacturing in Coburg, OR, USA, 2018 From our publication.

Optimizing spray applications is necessary to address increasing pesticide expenses, limited labor availability, stricter regulations, and increased public awareness of pesticide use. For four years the Nackley Lab and Dr. Jay Pscheidt at OSU  have been collaborating with USDA-ARS, and the Fulcher group at the University of Tennessee to investigate application of a sensor-guided sprayer in horticultural systems. Sensor-based systems can apply a variable-rate spray that adapts to the changing canopy volume and density thereby reducing waste and off-target deposition compared with standard constant-rate sprayers.

Water sensitive spray cards are used to measure the coverage from applications by standard and sensor-based Airblast sprayers.

We tested the effect of variable- and constant-rate spray applications and phenological stage on spray volume, coverage, and deposit density in two perennial specialty crop systems: an apple orchard and a grape vineyard. Our research showed that the greatest differences in the volume of pesticide application between constant- and variable-rate sprayer modes occurred early in the season when the canopy was sparse. The standard spray mode discharged a constant volume regardless of the canopy characteristics causing pesticide spray to drift through the open canopies beyond the desired target. Reducing nontarget deposition is critical because aerial drift, ground spray, and runoff can contaminate surface and groundwater and have toxic effects on nontarget species. Unlike the standard spray mode, the Intelligent sprayer mode made real-time adjustments, decreasing the application volume when vegetation was absent, which resulted in a more targeted spray and decreased drift and off-target ground spray. Increasing spray efficiency is critically important because spray losses to the ground and aerial drift by constant-rate, air-assist sprayers can be 40% to 60% of total applied spray in orchards and 10% to 50% the total applied spray volume in vineyards.

Intelligent sprayer system in a red maple nursery.  https://agsci.oregonstate.edu/nursery/precision-spray-applications

If disease and arthropod control are not diminished, reducing the pesticide volume applied on a farm has multifaceted benefits. The most direct benefit, and usually the one that motivates the adoption of variable-rate systems, comes from a reduction in pesticide costs due to lower application volumes. Other research found variable-rate technology can reduce pesticide costs by as much as 67%. Reducing the amount of active ingredient per application also causes a concomitant decrease in environmental impact and worker exposure. Moreover, when the quantity of pesticide required to treat an area is decreased, additional efficiencies are realized from the reduced need to refill, such as lower fuel and labor costs, and improved ability to complete applications in windows of good weather. Additionally, requiring less water as in the case of lower spray volumes is beneficial for orchards and vineyards that have limited access to water.

More info:

Warneke, B.W., J. Pscheidt, and L.L. Nackley. 2021. How to do regular maintenance on air blast sprayers to ensure proper care for specialty crops. https://catalog.extension.oregonstate.edu/em9316

Warneke, B.W., J Pscheidt, R. Rosetta, and L.L. Nackley. 2019. Sensor Sprayers for Specialty Crop Production https://catalog.extension.oregonstate.edu/pnw727

Nackley L.L., B.W. Warneke, L. Fessler, J. Pscheidt, D. Lockwood, W.C. Wright, X Sun, and A. Fulcher. 2021. Variable-rate spray technology optimizes pesticide application by adjusting for seasonal shifts in deciduous perennial crops. HortTechnology 31 https://doi.org/10.21273/HORTTECH04794-21

Warneke,B.W., H. Zhu, J. Pscheidt, and L.L. Nackley. 2020 Canopy spray application technology in specialty crops: a slowly evolving landscape. Pest Manag Sci 77: 2157–2164

Irrigation: Tip the scales to efficient irrigation with mini-lysimeters

Dalyn McCauley

Highlights

  1. Nurseries grow a wide variety of species and use many different crop production methods which can make effectively scheduling irrigation difficult.
  2. Mini-lysimeters are devices that measure evapotranspiration (ET) via a change in weight of a containerized crop.
  3. 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-yard to 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

a mini-lysimeter being used for irrigation of hemp
An example of a mini-lysimeter being used to control irrigation of hemp at NWREC

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.

An exploded view of the mini-lysimeter assembly.
An exploded view of the mini-lysimeter assembly. The device has a footprint of 10 x 10 x 2in.

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.