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^Using Soil Moisture SensorsFor Efficient Irrigation In Greenhousespage 2by Marc Van Iersel and Stephanie Burnett

^Wireless Monitoring of WholesaleNurseries: Is it possible?page 4

Gauging the

Newsletter for thehorticulture, nursery,and greenhouse professional.

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IN THISISSUE

Green

GreenhouseBlueberriesGreenhouse

Seedling

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MANUAL IRRIGATION is labor-

intensive and repetitive, so it is oneof the first greenhouse tasks thatshould be automated. Although automating irrigation is easy,

automated systems are not necessarily waterefficient. Many growers use timers to controlirrigation, but timers do not account for day-to-daychanges in plant water use caused by naturalfluctuations in temperature, light and humiditylevels. In addition, plant water use increases asplants grow. This makes it difficult to obtainefficient irrigation using a timer. Given the

increasing strain on water resources in many partsof North America, the greenhouse industry needsto move towards more efficient irrigation systems.

Soil water sensors provide promising newopportunities for automating greenhouse irrigationaccording to plant need. We have workedextensively with Decagon Devices’ EC-5 probes,

Using Soil Water Sensors ForEfficient Irrigation In Greenhouses

Marc van Iersel andStephanie Burnettwith the University ofGeorgia

Figure 1. The water content of the substrate over thecourse of the experiment. Irrigation was controlled usingEC-5 probes, and a small amount of water was added tothe substrate automatically whenever the substrate watercontent dropped below the irrigation set point. There wereeight different treatments with set points ranging from 5to 40%.

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Figure 2. The effect of the substrate water content (left) and thetotal irrigation volume (right) on the dry weight of petunias.Controlling irrigation by controlling the substrate water contentproved to be an effective way to control plant growth.

the substrate water content in a particularcontainer had dried out to the irrigation set

point, our automated irrigation systemstarted irrigating that tray. The water content

of the substrate generally was kept slightlyabove the set point.

A higher substrate water set point for irrigationresulted in more frequent waterings. Although theirrigation quantity increased with increasingsubstrate water levels, there was no leaching in anyof the treatments. Even the largest plant receivedonly 650 mL (about 21 fl. oz.) of water during thelast 20 days of the experiment. Daily water use inthe treatment with the highest water use rangedfrom only 15-20 mL/plant/day (just over onetablespoon!) when the plants were small to 45 mL/plant/day (3 tablespoons) at the end of theexperiment.

Plant growth increased with increasing substratewater content, but there was little differencebetween the 25, 30, 35, and 40% treatments (Figure2 left, 3). Since plant growth was highly correlatedwith the amount of water the plants received (Fig. 2right), controlling irrigation based on substrate

which are small enough to fit into a4” pot, and have found that theseprobes accurately measure thevolumetric water content of soillesssubstrates. We have integrated EC-5 probesinto an automated irrigation system that makesit possible to irrigate plants based on actual plantwater use.

The basic idea behind using soil water sensors tocontrol irrigation is simple: when plants use water,they take it up from the substrate, so the watercontent of the substrate decreases. Soil watersensors detect these changes and can be used toopen an irrigation valve when the substrate watercontent drops below a user-determined set-point.This results in frequent applications of smallamounts of water, and the frequency of irrigation isadjusted automatically based on the rate ofsubstrate water depletion. This irrigation approachautomatically replaces water that is used by plantsor lost through evaporation and assures that plantsare never exposed to drought stress. By irrigatingwith the amount of water actually needed by theplants, water use and leaching can be reducedgreatly. This minimizes pollution without usingexpensive recycling irrigation systems or largeponds to capture runoff.

Does it really work?

To test this irrigation approach and todetermine how much water petunias need forgood growth, we grew them at substrate waterlevels ranging from 5 to 40%. Irrigation wascontrolled with EC-5 probes in the substrate,which were connected to a datalogger. For thefirst nine days after transplanting seedlings, allsubstrates were kept well-watered to allow theplants to establish. Afterwards, our irrigationsystem maintained substrate water content(treatments ranging from 5-40%) for 20 daysand then plants were harvested.

Our irrigation system performed very wellthroughout the entire study (Fig. 1). As soon as MORE PAGE 6 Z

[ Petunia (Petunia Hybrida)

Petunias come in every color exceptorange. Petunias are part of thenightshade family, which also includestobacco and tomato.

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REMEMBER THE DAYS when you ranback and forth between your office andyour plants to check the moisture and temperature of your growth

medium? Nursery and greenhouse managers withsmaller operations may be able to get away withthis method. However,managers of large facilitieswill often spend manyhours a day checkingenvironmental conditionsin multiple fields andgreenhouses. Fortunately,new tools have been createdto help nursery andgreenhouse managersmonitor environmentalparameters from thecomfort of their desks. One tool currentlyundergoing field trials is Decagon Devices’ newwireless ECH2O monitoring system, whichmeasures and monitors a variety of environmentalparameters. The ECH2O system is showingpromise as an innovative tool for managing large-scale greenhouses and nurseries.

Wireless Monitoring ofWholesale Nurseries:Is it possible?

_ The ECH2O-TE allows soil moisture,soil temperature, and bulk EC to bemeasured at the same location.

� More unused data logger ports foradditional environmental measurements.

� No calibration is needed for soilless media such aspotting soil, rockwool, and peat.

� Applications include plant sprouting and growthstudies, plant mortality prevention, and greenhousemonitoring.

_Charles McKay, in hisbook "Extraordinary Popular Delusionsand the Madness of Crowds”, tells astory of the time (1635):

A wealthy merchant had paid3,000 florins (280 poundssterling) for a rare SemperAugustus tulip bulb, and itdisappeared from his warehouse.After thoroughly searching hiswarehouse, he saw a sailor (whohad mistaken the tulip bulb for anonion) eating it. The sailor waspromptly arrested and spentmonths in jail.

Today, long-stem Parrot-typetulips sell for $24 for a bunchof ten.

X Lauren Bissey (Decagon)inserting ECH2O-TE sensor intoMaple sapling rootball.

Discuss these newsletter topicson the GREENHOUSE FORUM atwww.soil-moisture.org

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X Todd Martin (Decagon) andElise Ross (Bountiful FarmsNursery Manager) test ECH2Osystem communication using ahand-held PC.

Monitoring withSensorsand Dataloggers

One such field trial washeld at a wholesalenursery, BountifulFarms, in theWillamette Valley ofOregon. The ECH2Osystem was tested to seeif it could help theBountiful Farmsnursery manager

monitor water use across various fields. ECH2Osystems were installed in five fields and onegreenhouse in the spring of 2007 to determine ifsoil moisture sensors, which are typically used inresearch agriculture, could be used to understandwater use in nurseries and greenhouses. Eachsystem consisted of two ECH2O-TE sensors (soilmoisture, temperature, and electrical conductivity),one leaf wetness (LWS) sensor, a rain gaugemonitoring irrigation (ECRN-50), and a wirelessdata logger (EM50R), which transmitted data backto the nursery office via a Data Station. At anygiven time, the nursery manager could look at eachof the six locations on her office computer and seethe volumetric water content, EC, and temperatureof her pots.

Using the Data

To date, the nursery manager has been using thedata set from the five fields as a water managementtool. For example, the volumetric water contentdata are being used to determine if watering isreally occurring when the irrigation system isscheduled to turn on. More advanced use of thedata set includes determining how much water isenough for the plants while at the same timepreventing excess leaching from the pots. In thegreenhouse, an installation scheme which hasECH2O-TE sensors in both pots on the edges andthe interior of the greenhouse has allowed thenursery manager to ensure that the irrigation wateris being applied equally to all of the plants. The

_ Dolphinshrubs atBountifulFarms.

_ ECH2O system.

installation scheme has also allowed the manager toobserve the efficiency of the greenhouse wateringsystem.

Understanding Environmental Clues

Data, however, arenot only used toschedule or monitorirrigation. Forexample, bymonitoring the soiltemperature, thenursery managerwas able tounderstand how anovernight freeze hadaffected the roottemperature ofplants in both thenursery and thegreenhouses. Leafwetness sensorswere used todetermine if leaveswere staying wet fortoo long, thusincreasing chance

for disease. Decagon is currently working onrecommendations to nursery and greenhousemanagers on how to use the bulk ECmeasurements taken by the ECH2O-TE sensors asa tool in fertilizer scheduling. Possibilities arelimited only by the grower’s creativity. �

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water content may be a feasible method forcontrolling growth of rapidly elongating plants.

How can growers use this?

Several brands of greenhouse control systems canmeasure EC-5 probes, and could be used toautomate irrigation based on these measurements.Growers should check with the manufacturer oftheir control system to see if it can measure theseprobes. For growers who prefer a stand-alonecontroller, we have collaborated with Brower

ElectronicsLaboratories(Pittsboro, NC) todevelop a controllerthat can irrigate plantswhen the substratewater content dropsbelow a grower-determined set point(Figure 4). Thiscontroller also allowsgrowers to setirrigation duration anda minimum timeperiod betweensubsequent irrigations.

Growers who are notready to turn over

irrigation to soil water probes, could get valuableinformation about plant water needs by using EC-5probes with a handheld meter or datalogger fromDecagon. The handheld meter allows growers toplace sensors in some of their pots, and toperiodically measure the water content of thesubstrate. A datalogger can send data wirelessly toyour computer which allows you to monitorchanges in substrate water content in real-time

through graphical displays (see article on page 4.)Using this technology would give growers a muchbetter idea of how much water plants need, andwill help in making better irrigation decisions.

Conclusion

It appears that in the near future growers mayautomate irrigation using sensors to water plantsefficiently and improve plant quality. Thetechnology is currently available, and guidelines forits use are being developed. But, what’s next? Inthe future, we wish to gain a better grasp of howwater use changes depending on the location of acrop in the greenhouse (for example, proximity tocooling pads or fans), the number of plants grown,and environmental factors. An exciting newdevelopment is that the newer ECH2O-TE probescan measure substrate EC, soil temperature, andwater content. This may allow growers to controlboth irrigation and fertilization simultaneously. �

� Marc van Iersel is a professor in floriculture at theUniversity of Georgia; mvanier@uga.edu; for moreinformation, please visit Marc van Iersel’s irrigationautomation website: www.hortphys.uga.edu/irrigationcontrol.html

� Stephanie Burnett is an assistant professor infloriculture at the University of Maine;stephanie.burnett@umit.maine.edu

X Figure 3. The effect of substrate water content on the growth of petunias. The picture was taken after aone-month growing period. Irrigation was controlled usingEC-5 probes during the last 20 days of the trial.

X Figure 4. We developed an automated irrigationcontroller in cooperation with Brower ElectronicsLaboratories. This controller uses 1 to 4 ECH2O

EFFICIENT IRRIGATION YCONTINUED FROM PAGE 3

SUMMARY

� EC-5 sensorsaccurately measurevolumetric watercontent in soilesssubstrates.

� No water leachingoccurred in any ofthe treatments.

� Sensors can eitherbe used to controlirrigation or monitorwater use.

We gratefully acknowledge the Fred C. Gloeckner Foundation for funding our research.

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X Decagon’s water content, temperature, and electricalconductivity probe wins the annual AE50 award foroutstanding innovations. This award is given to newproducts that save producers time, cost and labor whileimproving user safety and operating in an environmentally-friendly fashion.

Tradeshows

HortiFair10/9/07-10/12/07Amsterdam

International Irrigation Association12/6/07-12/11/07San Diego, CADecember 9, 2007 5 PM Dr. Colin Campbell presenting"Calibration and Evaluation of an Improved Low-Cost SoilMoisture Sensor"

Virtual Seminars1. Soil Moisture Sensors and Irrigation Control:

Separating Fact from Fiction(Irrigation Association credit is given for seminar #1.)

2. Steps to a Better Data Set:Installing Soil Moisture Sensors

3. Steps to a Better Data Set:Creating a Moisture Release Curve

4. Water Potential Soil and Plant Dynamics5. No Wires No Limits: Wireless System

Installation for Measuring Soil Moisture

Contact Decagon for more informationregarding these virtual seminars.

X The EC-5 soil moisture sensor was designed forgreenhouse growers.

� Size permits placement in small starter pots.

� Innovative sensor design is appropriate for both soiland soilless media with minimal EC effect.

� Applications include monitoring irrigation schedules,preventing plant water stress, and spatial variabilitystudies.

XGreenhouses are increasingly important in thefood supply of high latitude countries. The largestcommercial greenhouse complex in the world is inWillcox, Arizona, USA where 262 acres of hydroponictomatoes and cucumbers are entirely grown underglass at Eurofresh Farms.

The first modern greenhouses were built in Italy inthe sixteenth century to house exotic plants explorersbrought back from the tropics. They were originallycalled giardini botanici (botanical gardens). Theconcept of greenhouses soon spread to theNetherlands and then England, along with the plants.

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YOU MAY or may not have heard the name“Decagon Devices” when talking aboutgreenhouse and nursery management. Over

the past few years, we have been dipping ourinstrumentation toes into the greenhouse waters tosee if our products can help growers “talk” to theirplants. However, Decagon is not new to the field ofplant-soil-water interactions. In fact, DecagonDevices was founded in 1983 by soil scientistGaylon Campbell. The instruments that you havebeen hearing about over the past three years are theresults of twenty years of innovation, creativity, andhands-on experience. Decagon has been workingwith progressive research scientists all over theworld in testing soils instruments for use ingreenhouses and nurseries. Through this research,Decagon has perfected instruments that cater to theneeds of greenhouse and nursery growers.

To see if Decagon Devices instrumentation can helpyou manage your nursery or greenhouse, stop by atone of the tradeshows or visit our website athttp://www.decagon.com/irrigation/greenhouse.

Lauren Bisseyis the ECH2O productmanager at Decagon

Devices, Inc. Lauren has aunique perspective since

she was a former Decagoncustomer, utilizing

Decagon’s soil moisturesensors and porometer for

her own research.

Dr. Colin Campbellis the Research and

Development at DecagonDevices, Inc. He is also an

adjunct professor atWashington State

University teachingEnvironmental physics.Colin has a Ph.D. from

Texas A&M in Soil Physics.

Growers,Meet Decagon

_The EC-TM integratesvolumetric water content andtemperature, two fundamentalmeasurements needed for avariety of plant and soil studies,into one sensor.

� Temperature and soil moisture measured at the same location.

� Plug and play capabilities with EM50 logger.

� Applications include heated bed monitoring, plant sprouting and growthstudies, and greenhouse monitoring.

2365 NE Hopkins CourtPullman, Washington 99163

800-755-2751fax 509-332-5158

soils@decagon.comwww.decagon.com/echo

International 1-509-332-2756

GreenNewsletter for thehorticulture, nursery and greenhouse professional.

Gauging the

©2007 DECAGONPrinted in USA

_Hothouse tomato growers areconcerned with soil temperatureand production temperature forseed germination, vegetativegrowth, and fruit set.

DDECAGONDEVICES

Dr. Doug Cobosis the lead scientist/

enginer working with theJet Propulsion Lab to

develop a sensor designedby Decagon Devices onthe 2007 Mars Phoenix

Mission to measure waterand other surface

properties on Mars.

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