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Using Leaf Temperature for Irrigation Timing

Using Leaf Temperature for Irrigation Timing. Daniel L. Bockhold Graduate Research Assistant University of Missouri - Columbia Department of Biological Engineering. Methods of Irrigation Scheduling. Checkbook Methods Soil Moisture Sensors Evaporation Pans Crop Symptoms

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Using Leaf Temperature for Irrigation Timing

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  1. Using Leaf Temperature for Irrigation Timing Daniel L. Bockhold Graduate Research Assistant University of Missouri - Columbia Department of Biological Engineering

  2. Methods of Irrigation Scheduling • Checkbook Methods • Soil Moisture Sensors • Evaporation Pans • Crop Symptoms • Canopy Temperature

  3. Methods of Irrigation Scheduling • Woodruff Charts • Arkansas Scheduler • Michiana Scheduler • Gypsum Blocks • Tensiometers • Watermark Sensors • Washtub • Visual • Infrared Sensors

  4. Infrared Sensors • Measure leaf canopy temperatures, Tc • Warm leaf canopy temperatures indicate stress • Plant water-stress due to lack of water

  5. When to Irrigate? • Stress Degree Day (SDD) • Crop Water Stress Index (CWSI) • Temperature-Time Thresholds • Other?

  6. 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

  7. 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

  8. 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

  9. 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

  10. Evaluation Methods Five different treatments • 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

  11. 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)

  12. Calculation of Canopy Temperature • Assumes canopy temperature is equal to the temperature of a wetted leaf • Calculated from measured weather data

  13. Discussion of Calculation • Accurately predicts canopy temperature on most days • Under-predicts on days where humidity is low

  14. Diurnal Patterns Canopy Temperatures

  15. 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

  16. 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

  17. 2002 Cotton Results

  18. 2003 Cotton Results

  19. Soybean Canopy Temperatures • Well-watered treatment was not always the lowest temperature • Dryland treatment was not always the highest temperature

  20. 2002 Soybean Results

  21. 2003 Soybean Results

  22. Corn Canopy Temperatures • Well-watered treatment had the lowest average temperature • IR treatments had the next lowest temperatures and were in the same grouping

  23. 2003 Corn Results

  24. Option 1 • Tc greater than a calculated temperature for a given amount of time • Advantage • Detects stress faster • Disadvantage • Cost

  25. Costs – Option 1

  26. Option 2 • Tc greater than air temperature for a given amount of time • Advantage • Less expensive • Disadvantage • Not as responsive to stress

  27. Costs – Option 2

  28. Option 3 • Tc measured with handheld infrared thermometer greater than air temperature • Advantages • Inexpensive • Simple • Disadvantage • Measurements are taken by hand

  29. Costs – Option 3

  30. 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

  31. 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

  32. Questions ?

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