Using Leaf Temperature for Irrigation Timing Daniel L. Bockhold Graduate Research Assistant...
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Transcript of Using Leaf Temperature for Irrigation Timing Daniel L. Bockhold Graduate Research Assistant...
Using Leaf Temperature for Irrigation Timing
Daniel L. BockholdGraduate Research Assistant
University of Missouri - ColumbiaDepartment of Biological Engineering
Methods of Irrigation Scheduling
• Checkbook Methods
• Soil Moisture Sensors
• Evaporation Pans
• Crop Symptoms
• Canopy Temperature
Methods of Irrigation Scheduling
• Woodruff Charts• Arkansas Scheduler• Michiana Scheduler• Gypsum Blocks• Tensiometers• Watermark Sensors• Washtub• Visual• Infrared Sensors
Infrared Sensors
• Measure leaf canopy temperatures, Tc• Warm leaf canopy temperatures indicate stress • Plant water-stress due to lack of water
When to Irrigate?
• Stress Degree Day (SDD)
• Crop Water Stress Index (CWSI)
• Temperature-Time Thresholds
• Other?
Stress Degree Day
• Measured once a day (1-2 hrs after solar noon)
• Summed over many days
• Replaced by CWSI
• Problem – temperature difference varies with other climatic factors
CWSI
• Plotted as (Tc-Ta) vs. VPD• Tmax is non-transpiring crop• Tmin is non-water-stressed crop• Problem – difference between Tmax
and Tmin is small at low VPD
-6-5-4-3-2-101234
0 1 2 3 4 5 6
Vapor Pressure Deficit (kPa)
Tc-
Ta
(oC
)
Non-water-stressed Baseline Non-transpiring Baseline
Temperature-Time Thresholds
• Irrigate when Tc is above an ideal canopy temperature for a given amount of time
• Problem – in humid conditions, Tc will rise higher than the ideal temperature without being water-stressed
Methods We Used for Scheduling
• Tc greater than a calculated temperature for a given amount of time
• Tc greater than air temperature for a given amount of time
Evaluation Methods
• Well-watered treatment (100%) replaced water used with biweekly irrigations
• Semi-stressed treatment (50%)• 2002 – received half the amount of water
of the 100%• 2003 – received half the calculated ET
minus rainfall
• Dryland treatment received only rainfall
Five different treatments
Evaluation Methods(Cont.)
• (IR1) irrigated 1 inch when Tc was greater than calculated temperature for 3 hours on 2 consecutive days
• (IR2) irrigated 1 inch when Tc was greater than Ta for 3 hours on 2 consecutive days (2003 only)
Calculation of Canopy Temperature
• Assumes canopy temperature is equal to the temperature of a wetted leaf
• Calculated from measured weather data
Discussion of Calculation
• Accurately predicts canopy temperature on most days
• Under-predicts on days where humidity is low
Diurnal Patterns Canopy TemperaturesSurface Temperatures (Cotton-2002)
15
20
25
30
35
224 225 226 227
DOY
Te
mp
era
ture
(oC
)
100%IRDryTs-cal
CloudCover
Irrigation of IR Treatment
Rainfall
Canopy vs. Air Temperature
• Comparing canopy temperature to air temperature is simpler and requires less instrumentation
• Problem – Average canopy temperatures of the well-watered crops were less than air temperature
• Result – Under-irrigation could occur
Cotton Canopy Temperatures
• Dryland was always in grouping with highest average temperature
• IR treatments were in the same or lower temperature grouping as the well-watered treatment
2002 Cotton Results
Treatment Yield (lb/ac)
Irrigation (in)
IWUE (lb/ac-in)
100% 842 7.2 1.25
50% 1003 3.6 47.2
IR1 1092 3.0 0.397
Dryland 833 0.0 -----
2003 Cotton Results
Treatment Yield (lb/ac)
Irrigation (in)
IWUE (lb/ac-in)
100% 1137 5.8 35.5
50% 897 0.7 -48.6
IR 1 1063 4.7 28.1
IR 2 1037 3.3 32.1
Dryland 931 0.0 -----
Soybean Canopy Temperatures
• Well-watered treatment was not always the lowest temperature
• Dryland treatment was not always the highest temperature
2002 Soybean Results
Treatment Yield (bu/ac)
Irrigation (in)
IWUE (bu/ac-in)
100% 50 13.5 -0.37
50% 54 6.8 -0.15
IR1 52 4.9 -0.61
Dryland 55 0.0 -----
2003 Soybean Results
Treatment Yield (bu/ac)
Irrigation (in)
IWUE (bu/ac-in)
100% 41 5.1 0.20
50% 45 0.8 6.25
IR 1 41 3.0 0.33
IR 2 46 2.7 2.22
Dryland 40 0.0 -----
Corn Canopy Temperatures
• Well-watered treatment had the lowest average temperature
• IR treatments had the next lowest temperatures and were in the same grouping
2003 Corn Results
Treatment Yield (bu/ac)
Irrigation (in)
IWUE (bu/ac-in)
100% 159 7.9 9.11
50% 84 1.7 -1.76
IR 1 136 3.3 14.85
IR 2 122 3.6 9.72
Dryland 87 0.0 -----
Option 1
Tc greater than a calculated temperature for a given amount of time
• AdvantageDetects stress faster
• DisadvantageCost
Costs – Option 1
Instrument Cost
Datalogger setup $2260
Air Temperature and RH $545
Solar Radiation $275
Wind Speed $195
IRTs $430
Total $3705
Option 2
Tc greater than air temperature for a given amount of time
• AdvantageLess expensive
• DisadvantageNot as responsive to stress
Costs – Option 2
Instrument Cost
Datalogger setup $2260
Air Temperature $70
IRTs $430
Total $2760
Option 3
Tc measured with handheld infrared thermometer greater than air temperature
• AdvantagesInexpensiveSimple
• DisadvantageMeasurements are taken by hand
Costs – Option 3
Instrument Cost
Handheld IRT $100
Air Temperature $30
Total $130
Conclusions
• Irrigation scheduling based on canopy temperature can be used in humid regions with certain restrictions
• Calculated canopy temperature accurately predicted the measured canopy temperature when the humidity was high
• Comparing canopy to air temperature can be useful, but may cause under-irrigation
Conclusions (Cont.)
• Yield results showed no statistical difference in treatments of cotton and soybean, but did in corn
• Different setups can be made using infrared thermometers that vary in cost
Questions ?