Information About Tensiometer

Tensiometers measure how easily water can be drawn out of the soil. They consist of a ceramic tip that absorbs water, a clear tube that holds air, absorbed water and the partial vacuum created by the two, and a gauge that shows how strong the vacuum is. The more water absorbed from the soil, the weaker the vacuum will be. Farmers use tensiometers to see how easily their plants can absorb water through their roots.

  1. Definition

    • A tensiometer measures the water retention and soil moisture tension of soil. It shows scientists, researchers and farmers how easy it is to pull water from the soil. By using a vacuum to draw water out of the earth, it gives a direct reading on the matric potential, or the force of gravity and molecular bonding that must be overcome for roots or pipes to accomplish the same feat.

    Materials

    • The tensiometer is created from a long tube made of glass or plastic. This is the tube into which the water is drawn. One end is tipped with a ceramic covering, porous enough to let water through, while the other end has some type of vacuum gauge that measures the pressure within the tube.

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    Process

    • The tensiometer is planted into the soil, with the ceramic tip at the depth the user wants to analyze. Most tensiometers are a foot or a couple feet in length, but there are mini-tensiometers available that measure the surface soil moisture tension by extending down only 1/2 inch. The tensiometer is left in the soil as the moisture dries out. The ceramic tip will absorb moisture like a plant's roots, while the tube will partially fill with water and create a vacuum. The gauge will measure and display readings on the strength of the vacuum, which will show how dry or moist the soil is and how easily water can be pulled from it. If the soil is moisturized again by irrigation or rainfall, more water is absorbed into the tube, and the vacuum will be reduced.

    Uses

    • Farmers use tensiometers to set up irrigation schedules for their plants, especially in dry seasons. Using the readouts, they can judge how easily their plants can draw up water with their roots and how long water can be absorbed after the soil is moisturized. This gives them a good idea about how much water to give their plants and at what intervals. Scientists use tensiometers to measure natural moisture tension in different areas of the world to see how plants get their moisture and the types of growing environments their roots prefer.

    Considerations

    • Tensiometers have a limited area of reliability. They generally do not operate well in very dry soils or desert conditions, since some amount of water must be available in the soil. At times, air bubbles can enter the tube, causing false readings. Tensiometer readings should also not be taken as an accurate portrayal of the entire landscape, since tensiometers can only measure water directly in the soil in which they are planted.

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20th Jan 2015

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