Soil Moisture Sensors

Hydra Probe Soil Moisture Sensor | Industry leading soil moisture, temperature, and conductivity measurement

The Stevens Hydra Probe represents the most advanced and robust soil moisture sensor on the market today. Utilizing patented technology and a 50MHz frequency, the Hydra Probe delivers very accurate measurements of soil conditions, including:

Common installation scenarios see the Hydra Probe being buried in the soil (referred to as “in-situ” placement) at several different depths in order to measure soil parameters over a wide area. Downloading the data to a computer and looking at the results gives the user very detailed information about current soil conditions.

For more information about soil monitoring, including an overview of different types of sensors, soil types, applications, and more please visit, a great resource for soil monitoring information.

The benefits, features, and applications of the Hydra Probe soil moisture sensor:

  • Instantly measure soil moisture, electrical conductivity/salinity, temperature, and more
  • Optimize soil analysis and irrigation
  • Enables measurement of native (undisturbed) soil
  • Low risk: 10 years of field-proven science
  • Measure flow and movement of the wetting front through a soil profile
  • Preforms well in high-salinity soils
  • Easier monitoring of remote sites
  • Review real-time soil data and trends from the office
  • Instantaneous sensor response time
  • Serial addressable: multiple units on one cable
  • Maintenance-free
  • Easily linked to wireless systems
  • No calibration for mineral soils
  • Custom calibration available for peat, grain and organic soils
  • Compatible with most data logging systems
  • Digital or analog output
  • Compact & rugged for years of in-soil use
  • Long/short-term soil monitoring
  • Spot checking of soil
  • Golf & sports turf management
  • Precision agriculture/fertigation
  • Geotechnical measurement
  • Weather/climate studies
  • Agriculture research
  • Soil & ground water remediation
  • Flood control forecasting
  • Forecasting forest tinder conditions


The Hydra Probe soil sensor is sold as two basic models, the original Hydra Probe with analog output, and the Hydra Probe II that features either an SDI-12 or RS485 output. The following matrix compares and contrasts the difference between the models:

Probe type Hydra Probe - Analog Hydra Probe II - SDI-12 Hydra Probe II - RS485
Output 4 voltages Up to 17 processed
engineering units of meaure
and/or 5 voltages
Up to 17 processed
engineering units of meaure
and/or 5 voltages
Temperature Accuracy +/- 0.6° C +/- 0.1° C +/- 0.1° C
Temperature Range -10° to +55° C -10° to +55° C
(optional -30° version available)
-10° to +55° C
(optional -30° version available)
Conductivity 0.001 to 1.5 S/m 0.001 to 1.5 S/m 0.001 to 1.5 S/m
Soil Moisture Completly dry to fully saturated Completly dry to fully saturated Completly dry to fully saturated
Dielectric Constant +/- 1.5% or +/- 0.2
whichever is greater
+/- 1.5% or +/- 0.2
whichever is greater
+/- 1.5% or +/- 0.2
whichever is greater
Power Requirement 7 - 30 VDC 7 - 30 VDC 7 - 30 VDC
Power Usage Typically 20 mA
40 mA max
<1 mA idle
30 mA active
<10 mA idle
30 mA active
Cable Length Up to 100 ft. max Up to 164 ft. max Up to 4,000 ft. max
Cable Specs 7 wire: color-coded
18 AWG copper wire
3 wire: power, ground & data 4 wire: power, ground,
com+, com-
Probe Length 4.9 in 4.9 in 4.9 in
Probe Diameter 1.6 in 1.6 in 1.6 in
Probe Weight 200 g 200 g 200 g


Other Soil Monitoring Solutions

POGO Portable Soil Sensor

The Stevens POGO Portable Soil Sensor puts the power the Hydra Probe II soil sensor in the palm of your hand. Instantly measure 21 soil parameters wherever you go, no pre-installation of equipment necessary. Logging and downloading the sampled data to a computer for future analysis is a snap with the included PDA and HydraMon software.

Hand Held Hydra Data Reader for Analog Hydra Probe

The Stevens Portable Hydra Reader is designed for teams using or requiring analog output from the Hydra Probe soil sensor systems. The Hydra Reader acquires, displays, and logs data directly from the Hydra Probe. The Hydra Reader converts raw Hydra Probe voltages directly into soil moisture, salinity, and temperature readings without requiring any further processing or calibration. Data can then be logged, stored and downloaded to a PC for analysis, or the unit may be put in direct read only mode.

The Hydra Reader downloads data to a PC for archiving, graphical presentation, and report generation. Software makes downloading simple and the data may be customized to specific user needs.

The Hydra Reader is a compact, lightweight package that has no maintenance requirements.



Other Information