The SOILSPEC Tensiometer is a simple instrument used to provide a direct indication of how difficult it is for your crop to extract moisture from the soil. It has 
a porous ceramic tip at the bottom and a rubber stopper in the top. This tube is then filled with water.

As the soil dries out, the surface tension in the surrounding soil attempts to draw the water out of the tube through the ceramic tip. The rubber stopper in the end makes extraction of water impossible. The surface tension at the ceramic tip creates a pressure reduction in the air space at the top of the tube. High suction is caused by dry soil. Low suction is caused by moist soil. Using a vacuum gauge to measure these suction levels is a very SIMPLE, very EFFECTIVE method of checking soil moisture. What's more, it indicates directly how much water is available to your crop. Tracking these readings over a period of time paints a picture of what exactly is happening in the soil.