Application of IoT Soil Moisture Sensing System

Background:

As demand for freshwater resources by variable sectors continues to grow, it is critical to improve irrigation planning to produce more crops per drop of water and reduce potential water loss. In the past, several methods for improving irrigation scheduling have been developed and implemented based on monitoring variables such as crop water use, soil moisture status, and crop canopy temperature. Among these methods, monitoring soil moisture has been studied and practiced for decades. Despite their long history, the use of soil moisture sensors to implement precise irrigation scheduling remains somewhat limited. This limited adoption may be due in part to the technical challenges users face when selecting soil moisture sensor systems and translating sensor readings into actual irrigation decisions. The purpose of this fact sheet is to help producers select the correct type of soil moisture monitoring equipment to ensure their investment produces useful information for irrigation planning. The topics discussed here can also help sensor manufacturers develop new equipment and improve existing equipment to better meet the needs of producers and crop advisors.

Point Sensors and Probes

Many available sensors provide data for a single point in the soil (a point in the soil profile) immediately surrounding the sensing components of the device. Therefore, a separate sensor must be installed for each layer (depth) of soil to be monitored along the soil profile. This can significantly increase the time and labor requirements for sensor installation. Other sensors stack multiple sensing devices on a post or probe (Figure 1). This design allows one probe to provide soil moisture data for multiple soil layers. Installing and removing probes typically requires less time and labor than point sensors. Soil moisture probes are commercially available in a variety of types, lengths, and the number and spacing of sensing elements on the probe. For example, one brand offers 3-foot and 4-foot probes with sensors every 4 inches. The cost of a probe is usually a function of the length of the probe (longer probes are more expensive).

Sensor Accuracy

Different types of soil moisture sensors have different accuracies depending on the sensing technology they use and the properties of the soil in which they are installed. For example, electromagnetic sensor readings tend to have larger errors in soils with higher clay content. The salinity of the soil and/or irrigation water is another factor that can increase sensor error. The results of the field study conducted in Oklahoma showed that the combined effect of increased clay content and increased salinity on the accuracy of the readings was significant. However, different sensors responded differently to the same levels of clay content and salinity. Before choosing a soil moisture sensor,

summarize

Soil moisture sensors provide insight into the amount of water available in a crop’s root zone, allowing users to avoid under- or over-watering, both of which can negatively impact farm profitability and sustainability. When including soil moisture sensing systems in your irrigation decisions, several key factors should be considered:

Choose between point sensors and probes. Probes are generally easier to install and provide a more comprehensive picture of available water along their length.
Sensor accuracy, especially if the target field has high clay content or salinity.
Installation quality and location, should be free of gaps, in a representative location and away from agricultural machinery and irrigation systems.
Methods of accessing collected soil moisture data (wireless vs. manual) and the cost and convenience associated with each option.
The ability to easily and quickly translate collected data into irrigation decisions.