Soil water content can be measured at a field, catchment, or continental scale using satellite-based technology. It can also be measured over large areas using down-welling cosmic neutrons.
Figure 5 illustrates what happens when a positive and a negative plate are charged and the ions move in the soil. For the resistance method to work, one critical assumption is that the number of ions in the soil remains relatively constant. If the number of ions in the soil is not constant or we use the sensor in a different soil, accuracy becomes impossible because as the number of ions in the pore water changes, the ability for current to flow is altered, even when the amount of water has not changed.
This idea can be illustrated using a simple example. For a sensor to be used for more than wet/dry measurements, it needs to have a calibration that relates the sensor output (in this case, its resistance or its simple inverse: electrical conductivity) to volumetric water content.
Everything you need to know about measuring soil moisture—all in one place.
Download the researcher's complete guide to soil moisture—>
Six short videos teach you everything you need to know about soil water content and soil water potential—and why you should measure them together. Plus, master the basics of soil hydraulic conductivity.
Watch it now—>
Our scientists have decades of experience helping researchers and growers measure the soil-plant-atmosphere continuum.
Talk to an expert—>
Request a quote—>