Soil Moisture Sensors

Q. What are soil moisture sensors?

A. Soil moisture sensors are electronic devices that are installed in the soil profile, usually in the plant’s root zone, and provide the user with information related to the amount of soil moisture available to the plant. The information might be provided in terms of “percent soil water” or could be a measure of soil water tension in “kiloPascals” or “centibars”.

Q. What are the different types of soil moisture sensors?

A. A multitude of commercial sensors exit on the market, and fall into to two primary categories: tensiometric and volumertric (or capacitance). Capacitance probes use special capacitor related sensors to measure the volume of what in the total volume of soil-- a soil parameter called the dielectric permittivity. Tensio metric soil moisture sensors measure "matric water potential" or soil water tension. This is the amount of energy ('suction') that a plant's roots must exert to extract soil water.

Q. how do soil moisture sensors help with waer management?

A. The purpose of a soil moisture sensor is to monitor soil moisutre status, which allows the farmer to prevent plant stress by maintaining soil moisutre at optimal levels . Soil moisture sensors allow you to determine if there is adequate soil moisture for the crop, if the soil is drying or if the soil is very dry.

Q. how do i install a soil moisture sensor?

A. Each sensor or probe type requires an appropriate installation method. In general, soil moisture sensing equipment must be installed in the soil with good sensor to soil contact. If using individual sensors, a hole must be opened to the depth of interest and then the sensor is installed and soil back-filled into the hole using either a soil-water slurry or a soil-only approach. For probes, a hole is opened up deep enough for the entire probe length and to the depth of interest in the soil. Similarly, after the probe is installed, soil is back-filled into the hole using either a soil-water slurry or a soil-only approach. Some probes are now installed with a dry install where the hole is opened to nearly the exact dimensions of the probe which is then pressed into the hole, requiring no back-fill.

Q. can i link my soil moisture sensor to my pivot to irrigate when dry?

A. From what we understand, currently you cannot link your soil moisture sensors to your center pivot to automatically start the pivot based on soil moisture status. Manufacturers certainly offer the ability to read soil moisture sensors through their control panels, but not automatically start a system. Drip irrigation offers this option.

Q. how many sensors should be installed in a field?

A. If your field is highly variable, it would be good to install sensors in 2 to 4 sites in the field to give you information on soil moisture status in the difffent soil zones in the field. If cost is a major factor or if your field has a single, uniform soil (we rarely see this), then you could install a sensor system in a single location in your field.