Soil is an important natural resource, just as the air and water that surround us are. Unfortunately it has been overlooked in the past and taken for granted with disastrous results, such as the North American dust bowl of the 1930s. Today, the role of soil health on our climate as a whole is taken more seriously, with researchers at organizations such as the USDA-ARS (US Department of Agriculture, Agricultural Research Service) looking into how exactly soil interacts with the rest of our environment.
Because of on-going research and general interest in soil health and sustainability growing every year, monitoring soil in a more substantial and quantifiable way is becoming more important. In the past, monitoring the soil meant going out and physically handling the soil, taking samples, and comparing what was found to existing knowledge banks of soil information.
While nothing will replace actually going out and handling the soil for basic information, today's technology makes it possible to remotely monitor soil and track parameters that simply can't be easily or quickly measured by hand. Soil probes are now extremely accurate and offer an unparalleled look at what is going on below the surface. Giving instantaneous information on soil moisture content, salinity, temperature, and more, soil sensors are an important tool for anyone involved with soil, from a small-town farmer trying to increase his crop yield to researchers looking at how soil retains and off gases CO2. More importantly, just as computers have increased in power and dropped in price due to economies of scale, advanced soil measurement systems can be found at prices that are affordable for everyone.
In order for any soil probe to work, no matter the type, it must make contact with the soil. The most accurate soil probe will be fully surrounded by the soil, with no gaps or air holes between the probe and the soil. The probe then sends electrical signals into the soil, measures the responses, and relays this information to a data collection device known as a data logger. Read about the different types of soil sensors and the technology behind them.
What makes the information from soil sensors so valuable is that you are able to install multiple probes in the same area, each one buried below the last. This gives you an idea of what water is doing as it moves down through the different layers of soil (known as soil horizons). This information can be utilized in several ways, but here are two examples below:
In order to irrigate a particular crop at the optimum level, a farmer would install several probes in one location. One probe would be placed just below the surface of the soil, one in the root zone, and one below the root zone. When water is applied to this soil, these sensors reveal data about how quickly the water penetrates down through the soil, if it stagnates are certain depths, and other related information. By knowing how long it takes for the water the reach the root zone, the farmer can adjust his irrigation schedule accordingly. Furthermore, by seeing if any of the water is making it down below the root zone (where it can no longer be reached by the plants roots), the farmer can water less, saving money. Plants perform poorly under stress (too much or too little water), so optimizing irrigation schedules can not only lead to bigger yields but a cost savings in less water waste and a lower water bill.
Research scientists who study the earth and its environmental processes oftentimes need a way to visualize what is going on below the surface. For example, the Portland State University Department of Geology in conjunction with the USGS (US Geological Survey) is studying land slides in the steep west hills of Portland, Oregon. Using several Stevens Hydra Probes buried in different soil horizons, they are able to chart how water is moving between the layers of soil. After charting information during the wet season and analyzing it in Excel, they can see what types of soil absorb water more readily and which do not; in essence, showing them how much rain will cause a wasting event in specific soil types.