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Winter High Tunnel Environments: Managing and Monitoring
Illinois Specialty Crop ConferenceSpringfield, IL
January 8, 2020Liz MaynardDept. of Horticulture and LA, Purdue Universityemaynard@purdue.edu219-548-3674
E. Maynard, 2020Purdue University is an equal access/equal opportunity institution.
Purdue University is an equal access/equal opportunity institution.E. Maynard, 2020
• Solar radiation / light• Temperature• Relative humidity (RH)
The Environment
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•Photosynthesis•PAR measured in µmol / m2 / second•DLI measured in mol / m2 / day
Light
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0
5
10
15
20
25
30
9/24 10/20 11/15 12/11 1/6 2/1 2/27
Daily
Ligh
t Int
egra
l (m
ol/m
2/da
y)Daily light integral (DLI) in an unheated high tunnel in Northern Indiana in
fall and winter 2015 - 2016
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Time of Year Influence on Light
0
5
10
15
20
25
30
35
40
September October November December January February March
DLI (
mol
/m2/
day)
Expected DLI in fall and winter for representative locations in Northern, Central, and Southern Indiana
Northern Central Southern
J F M A M J J A S O N D J
Hours of Daylight
10
12
14
DLI estimate from 1998-2012 solar radiation, Faust and Logan, 2018.
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Orientation
High Tunnel Structure and Light
North South
NorthNorth
South
South
• Orientation• Shape• Covering• Shade
ShapeCovering
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High Tunnel Covering
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Photosynthetically Active Radiation in High Tunnels and Solar Radiation at Pinney Purdue Ag Center, July 7-13, 2018
Plastic removed on July 9
New plastic
installed on
July 12
ET MaynardSolar radiation data obtained from iclimate.org, 7-17-2017.
Purdue University is an equal access/equal opportunity institution.E. Maynard, 2020
ET Maynard
Daily Light Integral in High Tunnels and Solar Radation at Pinney Purdue Ag Center, July 7-12, 2018
Solar radiation data obtained from iclimate.org; 7-17-2017. Two missing data points for 7/10 estimated based on PAR levels at HT 1.
E. Maynard, 2020Purdue University is an equal access/equal opportunity institution.
• Consider single layer plastic• Remove snow/ice• Remove shade sources• Remove row covers during the
day• Supplemental light?
Managing Light
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Managing Light
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Shade from Row Covers
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Shade From Row Covers
Row Cover Off Row Cover OnDaily Light
Integral (DLI)DLI Inside as % of
Daily Light Integral (DLI)
DLI Inside as % of
Date Outside Inside Outside Date Outside Inside Outside(mol/m2/day) (mol/m2/day)
12/01/16 4.2 2.9 69% 12/11/16 5.1 2.3 46%01/24/17 4.0 2.9 73% 01/28/17 3.9 1.9 48%02/11/17 13.1 10.2 78% 02/04/17 12.8 6.5 51%02/13/17 27.1 19.3 71% 02/09/17 27.5 13.2 48%03/24/17 37.1 24.7 67% 03/15/17 38.9 19.2 49%Average 72% 48%
Row cover 0.55 oz./sq. yd. spun-bonded polyester
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• Plant growth• Optimum• Base• Average daily temp and
growing degree days • Low temperature injury• High temperature injury• Influences on seed dormancy,
flowering, bolting• Soil temperature
Temperature
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Energy Flow and Storage
Energy exchange between a greenhouse and the surroundings, showing the sun as the main source of energy. (Adapted by M. O’Donnell from Figure 4-1, Aldrich and Bartok, 1989)
Infra-red thermal radiation from atmosphere
Infra-red thermal radiation from surfaces
Air exchange through vents
TranspirationEvaporation
Infra-red thermal radiation from plants
Reflected sunlight
Reflected sunlight
Sun
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Energy Flow and Storage
Heat loss from a greenhouse. (Adapted by M. O’Donnell from Figure 4-2, Aldrich and Bartok, 1989)
Radiation to cold sky
Infiltration (cold air)
Exfiltration (warm air)
Convection
Conduction into ground
Conduction to air
Cold outside air
Perimeter conduction
Convection
Cold sky
Mean Temp
Solar Radiation and DLI
19
Average Temperature and Daily Light
RR_min_air-tempWITHOUTHEATED-vs-date-overlayRR_daily-radiation-and-DLI-graph 63
Min. Daily Air Temp Outside and In – Determines what will survive
Daily Solar Radiation and Light
Outside
Minimum temperature determineswhat will survive
Under row cover 5-10°F warmer than above, 10–20°F warmer than outside
Daily Minimum Air Temperature Outside and in High Tunnel (unheated) and Low Tunnel,RR, 2015-2016
RR_ave_soil-temp-vs-date-overlaySepMarRR_daily-radiation-and-DLI-graph
Daily Solar Radiation and Light
69
Air temp and solar radiation in Feb. Data from CB, 2016
Air Temperature and Solar Radiation for a Week in February 2016
Air temp in tunnels increases quickly when the sun comes out.
Air under row cover in tunnel
Air above row cover in tunnel
Air outside
64
Air temp and SR in Feb, 1 day Data from CB, 2016
Temperature Increases Quickly When the Sun Comes Out!
Air under row cover in tunnel
Air above row cover in tunnel
Air outside
Data from Clay Bottom, 2016 65
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•Maximize light• Increase heat sinks• Dark mulch• Raised beds•Moist soil
•Reduce losses• Double layer poly, IR poly• Sealing gaps• Insulation•Windbreaks• Row covers
Temperature: Keeping it Warm
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• Spun-bonded polyester• Light, medium, heavy weight
Row Covers to Trap Heat Near Crop
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•Plant water relations• Leaf size and thickness, physiological disorders•Disease
Relative Humidity
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Time of Year Influence on Light, cont.
20
30
40
50
60
70
80
°F
Air Temperature, Unheated
50
60
70
80
90
100
110R
H %
Relative Humidity, Unheated
Relative humidity was near 100% at night and decreased as the tunnel warmed up during the day.
In early afternoon, relative humidity dropped quickly and so did temperature; the tunnel was vented to let in cooler outside air, which was also drier. If a row cover was present it may have been removed also.
Relative humidity and air temperature in unheated high tunnel in northern Indiana on Feb. 17, 2016.
12 AM 4:48 AM 9:36 AM 2:24 PM 7:12 PM 12 AM
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• Vent• Automation very helpful
• Remove row covers during day• Manage drainage
Relative Humidity
A Draft Framework for Thinking About Environmental Management
Time of Year Mode DangerSept. – Oct. growth, acclimating overheating
Nov. slow growth cold injury
Dec.-Jan storage, surviving, veryslow growth
cold injury, disease
Feb. – Mar. slow to faster growth cold injury, overheating, unwanted bolting
April growth overheating, unwanted bolting
60
Managing the Environment – Standard Daily/Seasonal Practices
• Watch forecast. Not just daily, but leading up to harvest to anticipate ideal windows for harvest. Monitor internal temperatures (if you have sensors)
• Anticipate venting and row cover removal in late morning and closing/covering in afternoon for temperature and RH management. Uncover to reduce RH, and increase solar radiation gain to soil. Vent to reduce RH, limit high temp.
• Multiple layers of row cover may be needed incrementally as temperatures drop.
• Do NOT remove covers early after freezing nights or you risk damaging plant tissue.
75
Managing the Environment – Standard Daily/Seasonal Practices• Some growers leave peak vents slightly vented at all times. Little air
exchange will occur if no side wall or lower vents are open. Management is
then reduced to side wall venting and row covers.
• Remove snow or ice to limit structural stress
• Emergency heater for extreme low temp situations?
• Insulate end walls, and north walls?
• Row covers not typically used in minimally heated tunnels. Low temp
threshold set at ~28 F (depends on crops and your fortitude)
• Make close observations by crop, variety, weather conditions, mgmt., and
keep records.
• In fall keep tunnel vented to “harden” off or “acclimatize” the plants to low
temps until absolutely necessary to close. Don’t baby your plants!
76
Minimally Heated TunnelsBenefits
–Less hardy crops survive for more diverse mix in mid-winter–Faster growth means higher yield–No need for row covers
Heating systems–Air - unit heaters are common–Soil - hydronic, air-to-air, electric
Temperature Management–What temperature? 28? 33? 40?–Manage for average daily temperature instead of minimum?–Flexible based on sunny/cloudy weather?
Average temp: 22.6, 38, 37.5., 37.9. Total of hourly differences in temp vs unheated: 370, 358, 367.
USDA Virtual Grower – software for calculating greenhouse heating costs
77
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• Use trustworthy sensors• Place sensors properly• Record regularly and reliably• Review records periodically• Recordkeeping options• By hand• Data logger
Monitoring Environment
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• Thermometers, thermocouples, thermistors• Max/min thermometers and sensors• Remote data access• Internet data access• Placement• At crop level (just above)• At standard height• Watch out for shade, drafts• Protected from direct sun• Protected from heat buildup• In root zone: 2-4 inches
Temperature
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Radiation Shields
Holden et al., 2013. www.fs.fed.us/rm/ubs_other/rmrs_2013_holden_z001.pdfwww.youtube.com/watch?v=LkVmJRsw5vs
Purdue University is an equal access/equal opportunity institution.E. Maynard, 2020
• Hygrometer• Sensors often combined with
temperature• Observe condensation
Relative Humidity
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• PAR Sensor• for plants, preferred to photometer or
pyranometer• Instantaneous measurement• Daily Light Integral (DLI)• Placement• Just above crop• Avoid shade• Level
Light
Logger and solar panel at EP
Solar Radiation and Air Temp. Sensors at RR
Light (PAR) Air Temp., and Soil
Moisture Sensors at CB
78
Example output Tinyurl.com/ppacht1Tinyurl.com/ppacht2
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tinyurl.com/ppacht1tinyurl.com/ppacht2
Output from Hobo datalogger and sensors
(sensors not currently in correct position)
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Watchdog dataloggers with sensors
www.specmeters.com
The system we use is downloaded manually by connecting to computer. Proprietary software displays graphs and does some summary reports.Newer products include can include wireless data transfer.
Can view readout manually.
Button logger can monitor over period of time but not convenient to check information on a regular basis.
http://wirelesstag.net/
Wireless Sensor Tags - Info
Wireless Sensor Tag - Specs
http://wirelesstag.net/
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Wireless Sensor Tags - Output
Row cover on hoops
No row cover No row cover
Row cover on hoops
No row cover
Row cover on hoops
3-Sensor Temperature and Humidity Smart Home Environment System with My AcuRite
https://www.acurite.com/shop-all.html?&sensor_measurements=111
Accurite
https://www.acurite.com/environment-system-with-temperature-and-humidity-01059.html
https://www.acurite.com/multi-sensor-thermometer-with-3-temperature-sensors.html
• Acurite www.acurite.com• Davis Instruments www.davisnet.com• Extech www.extech.com• Hobo onsetcomp.com• Lascarelectronics www.lascarelectronics.com• Meter metergroup.com• Monarch monarchinstrument.com• Spectrum Technologies, Inc. specmeters.com• Wireless Tag wirelesstag.net
Some Suppliers of Environmental Monitoring Equipment
Thislistisnotmeanttobeall-inclusive.Inclusiononthelistdoesnotindicateendorsementnordoesexclusionindicatelackofendorsement.
Purdue University is an equal access/equal opportunity institution.E. Maynard, 2020
• Sunlight drives heat, soil is main heat sink• Vent and use row covers to manage temperature and RH• Learn the danger points (hot and cold) for your crops and conditions• Monitoring equipment available at reasonable cost, but line of sight
is a factor for wireless connections• Know what you want out of monitoring before investing money and
time• Stay informed about new materials, research on heating methods,
supplemental light
Managing and Monitoring Environment in Winter High Tunnels
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Michael O’Donnell, Purdue UniversityNathan Fingerle, River Ridge Farms
Ben Hartman, Clay Bottom FarmDavid Robb, Eden Prairie Farm
Thank you!Collaborators and Funding
This project was supported by a NCR SARE Partnership Grant through sub-award H004403722 to Purdue University from USDA Award 2014-38640-22156 to the University of Minnesota. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the USDA or the U.S. Government.
James FarmerAnalena Bruce Indiana University, BloomingtonThis project was supported by the U.S. Department of Agriculture's (USDA) Agricultural Marketing Service through grant (SCBG-15-002). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.
Erin A. Bluhm
Israel S. Calsoyas
Purdue University, HLA
HO-297 at edustore.purdue.edu
Horticulture & Landscape Architectureag.purdue.edu/hlaManaging the
Environment in High Tunnels for Cool
Season Vegetable Production HO-297-W
mdc.itap.purdue.edu/item.asp?Item_Number=HO-297-W
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