With all the different types of soil sensors and measurement technologies on the market and the different technologies that they employ, choosing the right one can be a confusing and time consuming process. Here we outline the different types of soil sensors available as well as their advantages and disadvantages.
Across the many different applications that soil sensors are used for, the primary attribute involved is soil moisture. Soil moisture sensors measure the volumetric water content in soil indirectly by using some other property of the soil, such as electrical resistance, dielectric constant, or interaction with neutrons as a proxy for the moisture content. The relation between the measured property and soil moisture must be calibrated and may vary depending on environmental factors such as soil type, temperature, and salinity (electrical conductivity).
Whereas soil moisture sensors measure volumetric water content, another class of sensors such as tensiometers and gypsum blocks measure water matric potential—the pressure it takes to pull water out of the soil.
Determining Soil Moisture Content Without Sensors
A variety of techniques are available for direct measurement of soil water content and most of them are based on the fact that water is removed from soil by evaporation, leaching, or chemical reaction. One of the most common methods of soil water content determination is gravimetric method with oven drying. This method involves weighing a moist sample, oven drying it at 105°C for 24 to 48 hours, reweighing, and calculating the mass of water lost as a percentage of the mass of the dried soil.