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Top > Soil Moisture Sensors > Hydra Probe II Soil Moisture and Salinity Sensor (SDI-12 / RS485)
Stevens Hydra Probe II Soil Moisture Sensor

Hydra Probe II Soil Moisture and Salinity Sensor (SDI-12 / RS485)

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PART #: 93640
PRICE: $395.00

Hydra Probe II Soil Moisture and Salinity Sensor (SDI-12 / RS485) Description

The Stevens Hydra Probe II soil sensor is an in-situ soil probe that measures 21 different soil parameters simultaneously with digital output. The Hydra Probe II soil sensor instantly calculates soil moisture, electrical conductivity/salinity, and temperature as well as supplying voltage outputs for research applications.

Stevens also offers an "Extended Temperature Range" version of the Hydra Probe II soil sensor which can measure down to -22° F (-30° C) for research, cold-climate, high-altitude, arctic applications or any other measurement situation where there will be significant below-freezing ground temperatures.

For more information on soil sensors such as the Hydra Probe II soil sensor and monitoring information, please visit


  • Instantly measure soil moisture, conductivity/salinity, temperature, and many other parameters
  • Optimize soil analysis and watering
  • Enables measurement of native (undisturbed) soil
  • Over ten years of field proven science
  • Measure flow of water from topsoil to sub-root zone
  • Performs well in high-salinity soil
  • Easier monitoring of remote sites
  • Review real-time soil data and trends from the office


  • Instantaneous sensor response
  • Serial addressable: multiple units on one cable
  • Maintenance-free
  • Easily linked to wireless systems
  • No calibration required for most soils
  • Compatible with most data logging systems
  • Digital or analog output
  • Compact, rugged for years of in-soil use - backed by a five-year performance warranty from Stevens

Hydra Probe II Informational Documents:
Dielectric Loss and Calibration of the Hydra Probe Soil Water Sensor
Evaluation of the Stevens Hydra Probe's Temperature Measurements from -30 to 40 Degrees Celsius
The Stevens Hydra Probe Inorganic Soil Calibrations
The Parameters of the Hydra Probe
Evaluation of Dielectric Constant-Based Soil Moisture Sensors in a Semiarid Rangeland
Measurement of Soil Water Content with a 50-MHz Soil Dielectric Sensor
Temperature Effects on Soil Dielectric Properties Measured at 50 MHz
Using Campbell Data Loggers with an SDI-12 Hydra Probe
Calculating Pore Water Electrical Conductivity From the Dielectric Permittivities of Soil
Connecting the Hydra Probe II to the Campbell CR10X Datalogger

Hydra Probe data add science to soil management for better understanding of soil conditions. The result is optimized analysis of soil for scientific study and for enhanced quality and yield of turf and crops.

Hydra Probe sensing technology has been deployed over 10 years by the USDA and is used by NASA for ground truthing of satellite-based soil imaging.

A compact, rugged design with potted internal components makes the Hydra Probe easier to deploy than competing sensors and ideal for remote and harsh conditions. Durable construction makes it possible for the units to remain in the field for many years, maintenance-free.

The defined sensing area allows accurate measurements in regions where there are strong soil moisture gradients, such as near the soil surface. Response time to changing soil conditions is immediate, and calibration is as simple as selecting a soil type (sand, silt, loam or clay).

Each Hydra Probe is serial addressable, allowing for multiple sensors to be connected to any RS485 or SDI-12 data logger via a single cable. Sensor data can also be sent directly to a radio modem through a small RS485-RS232 converter.

The Hydra Probe uses an electromagnetic signal propagated from the center tine of the probe to measure multiple parameters. The voltages recorded depend on the type of electrical properties of the soil. On-board software converts the raw voltage to standard units of measurement for each parameter. With a standard database or spreadsheet, managers can view real-time soil snapshots or long-term soil trends.

Applications include:

  • Long/short-term soil monitoring
  • Spot checking of soil
  • Golf green management
  • Sports turf management
  • Precision agriculture/fertigation
  • Geotechnical measurement
  • Weather/climate studies
  • Watershed management
  • Flood control forecasting
  • Forest tinder conditions
Required Feature(s)

Signal Output 
Cable Length 
Temperature Range 
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