What is a Soil Psychrometer?

A soil psychrometer, simply put, is an instrument used to measure water in the ground. You may be familiar with a regular psychrometer, which scientists and weather forecasters use to measure water in the air. The concept is the same, and both types of psychrometers are important and useful tools for not only scientists, but also for gardeners and farmers.

Water content in soil helps professionals learn when and how to plant crops. It is also important to learn a soil's water content when building an irrigation system. A soil psychrometer is especially useful in this situation, as the instrument is very accurate in dry conditions.

Soil psychrometers work by comparing two pieces of data. The instrument has two "bulbs," one that is 100% wet and one that is 100% dry. By comparing the two readings, you can get a value between 0.5 and 30, which can be converted into water content. The process is long, because you must wait for vapor equilibrium, and the readings are not as accurate when the soil is very wet, but the instrument is highly sensitive in dry conditions, making it a vital tool for farmers in arid regions.

Many alternatives are available for people who do not wish to use a soil psychrometer. One of the simplest ways to measure water content is to weigh exactly one pound of soil and then dry it out completely and weight it again. The difference between the two weights is water content. This method is not very accurate, but a good way for home gardeners to learn more about their soil conditions. A number of pieces of scientific equipment are available as well.

Before buying a water content reading device, know what is important to you. What are your soils' other properties? How accurate does the reading need to be? How humid is your climate? How much are you willing to spend? How much skill and experience in water content measuring do you have? After answering these basic questions, ask a professional at your local garden center to help you choose an instrument. There are many varieties of water content instruments, and only by answering the above questions you can decide if a soil psychrometer is right for you.