Accuracy of Soil Moisture Devices

1
Accuracy of Soil Moisture Devices

• Sanjay Shukla
• Agricultural and Biological Engineering
• UF-IFAS

2
Accuracy of Devices

• Factors
• Soil type (water holding capacity)
• Texture, organic matter, salinity
• Sandy soil
• Low plant available water (e.g. 5-6)
• Example 25 error sufficient to close to
  wilting point
• Soil specific calibration
• Silt and Clay
• Relatively less accuracy is acceptable
• Crop type
• Cost
• Type of device
• Not a big limiting factor with multi-depth
  devices

3
Examples of Types of Devices
4
Sensor Evaluation Preliminary ResultsExample
Purposes only Default Calibration - Not For
Distribution
5
Sensor Accuracy and Irrigation Scheduling

• Example
• Sandy soil with low water holding capacity
• Plant available water 6 , FC 9, PWP 3
• 25 error in measuring 6 PAW
• actual moisture 6 moisture read from sensor
  7.5 or 4.5 (under irrigation, adverse impact
  on crop)
• If errors are systematic
• can be calibrated for specific soil
• important for sandy soils
• errors can be substantially reduced
• calibration is time consuming
• calibrate with the gravimetric method data

6
Which Device Should I Use?

• Factors to consider
• Area of the farm and crop type
• Soil type and variability (texture, water holding
  capacity, types of soils within same farm)
• Accuracy - applicability of default calibration
  to your soil
• For coarse textured soils, better accuracy is
  needed
• Users comfort level and ease of use
• Maintenance requirement
• Cost (sensor, installation, and maintenance cost)
• Installation cost is high for short duration
  crops
• e.g. tomato, every 4-5 months

7
Which Device Should I Use?

• Using a soil moisture device, even inaccurate, is
  better than not using any
• If cost is a consideration, using handheld
  devices such as Hydrosense is a better option
• Soil specific calibration is important,
  especially for the coarse textured soils