Water Use and Plant Stress Monitoring Method Comparison

  Tule Actual ET Sensors Reference ET Weather Station Soil Moisture Sensors Sap Flow Sensors Aerial Imaging Pressure Chambers “Look & Feel”
Basic Operation Measures actual evapotranspiration in your field Measures evapotranspiration of a well-watered grass field nearby Measures environmental factors Measures soil water availability Estimates movement of water through trunk Broad scale visible and thermal images Measures leaf and stem water potential Look at plant appearance or feel soil
Provides Quantitative Measurement Yes No No No (unless rigorously lab calibrated) No (unless rigorously lab calibrated) No Yes No
Measures Plant Water Status Yes No No No Yes No Yes Yes
Monitoring Labor and Frequency Automatic, Daily Automatic, Hourly Automatic, Hourly Manual or Automatic, Hourly Automatic, Hourly Automatic, Weekly or less Manual, Infrequently Manual, Infrequently
Measurement Zone 1 to 10 acres Nearby, not in your field Many acres 2" from sensor Single Plant Many acres Single plant Single plant
Replacement & Maintenance Included None Annual calibration required 3-4 years , some require annual removal Included None Minimal None
Challenges Minimum measurement area is 1 acre.

ET is not measured in the grower’s actual field.

Crop coefficients can be inaccurate.

Does not measure crop stress.

Weather factors alone do not tell the grower about the water use or status of the crop.

Reference ET calculated from local weather factors provides inaccurate estimates for crop types other than well watered grass.

For crops with an extensive root zone (i.e orchards or vineyards), soil moisture measured at a particular depth may not be representative of available water.

Multiple devices required to represent field conditions.

Not applicable for all crop types.

Multiple devices required to represent field conditions.

It's too late. Once there is a decrease in greenness. There will be a reduction in yield that is unrecoverable.

Without turbulence measurements, imaging alone cannot tell the grower the water status of the crop.

Labor intensive.

Measurements can only be taken during narrow time windows.

Multiple measurements required to represent field conditions.

It's too late. Visual cues occur after growth has slowed.

Cannot reliably reproduce timing and degree of stress year after year.

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