A 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 special porous ceramic tip at the bottom and a rubber stopper in the top, (see diagram). This tube is installed into the ground where you want to measure the soil moisture and it is then filled with water.

HOW IT WORKS

As the soil dries out, the surface tension of the moisture in the surrounding soil attempts to draw the water out of the tube through the porous ceramic tip. However, because the tube is sealed with a rubber stopper, the water cannot escape. The suction at the ceramic tip then creates a pressure reduction in the air space at the top of the tube. Dry soil around the tip has a high suction. When irrigation or rainfall occurs, and the soil becomes moist, the tension (or suction) at the ceramic tip reduces, decreasing the vacuum at the top of the tube. If we use a vacuum gauge to read the vacuum level at the top of the tube, a high reading indicates that the soil is dry at and around the ceramic tip, and a low vacuum reading shows that the soil is moist. Simple, but very effective!!

What more, it indicates directly how much water is available to your crop.

By plotting the readings taken from a tensiometer over a period of time, it is easy to build up a picture of exactly what is happening in the soil.