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. 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 (T c -T a ) vs. VPD T max is non-transpiring crop T min is non-water-stressed crop Problem – difference between T max and T min 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 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

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 TreatmentYield (lb/ac) Irrigation (in) IWUE (lb/ac-in) 100%8427.21.25 50%10033.647.2 IR110923.00.397 Dryland8330.0-----

18. 2003 Cotton Results TreatmentYield (lb/ac) Irrigation (in) IWUE (lb/ac-in) 100%11375.835.5 50%8970.7-48.6 IR 110634.728.1 IR 210373.332.1 Dryland9310.0-----

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 TreatmentYield (bu/ac) Irrigation (in) IWUE (bu/ac-in) 100%5013.5-0.37 50%546.8-0.15 IR1524.9-0.61 Dryland550.0-----

21. 2003 Soybean Results TreatmentYield (bu/ac) Irrigation (in) IWUE (bu/ac-in) 100%415.10.20 50%450.86.25 IR 1413.00.33 IR 2462.72.22 Dryland400.0-----

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 TreatmentYield (bu/ac) Irrigation (in) IWUE (bu/ac-in) 100%1597.99.11 50%841.7-1.76 IR 11363.314.85 IR 21223.69.72 Dryland870.0-----

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 InstrumentCost Datalogger setup$2260 Air Temperature and RH$545 Solar Radiation$275 Wind Speed$195 IRTs$430 Total$3705

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 InstrumentCost Datalogger setup$2260 Air Temperature$70 IRTs$430 Total$2760

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 InstrumentCost Handheld IRT$100 Air Temperature$30 Total$130

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 ?