What is a Tensiometer?

✔️ A tensiometer is a tool used by farmers to monitor moisture in soil in which vegetables and fruits are grown.

✔️ Tensiometer readings are not influenced by changes in soil texture, temperature or salinity, and can operate without electricity, making batteries unnecessary.

✔️ A tensiometer is made of a delicate porous ceramic cup connected to a sealed, water-filled tube. It is best used when soil moisture is maintained at from 50 to 75 percent of field capacity, making it relevant mainly for crops such as corn or vegetables. Tensiometers do not measure the low moisture ranges of crops such as cotton, grains.

How will you know it’s time to irrigate?

  •  You’ll know it’s time to irrigate when tensiometer readings reach a predetermined value for the soil depth in which the concentration of food roots is greatest.
  • The duration of the irrigation is determined by tensiometers that measure soil tension at a second depth or more. If the tension readings at the second depth are low, a short irrigation time is indicated. Conversely, if they are high, the irrigation water should be allowed to flow until low readings are obtained.
  • The device is also used by farmers to determine the timing of greenhouse irrigation for pots and greenhouse beds, and is also used to determine rooting depth.
    – The readings can be continuously monitored, and rate of increase in soil tension at any given depth can be related to the density of the active roots.
  • The device continuously measures the potential soil water or tension, which is a measure of soil moisture or soil water content. If the soil tension is high, plants need to use more energy to produce soil water. If the soil tension is low, then plants have lower energy requirements for producing soil water.
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How are measurements taken?

  • – A tensiometer consists of a water-filled tube with a porous ceramic cup at the lower end. After it is installed in the ground, the water passes from the tensiometer through the cup and into the unsaturated soil.
  •  This process continues until the negative pressure inside it equals the negative pressure in the surrounding soil. The inner pressure is then in a state of equilibrium with the pressure in the soil and can be measured by reading a vacuum gauge on the tensiometer.
  •  When the wet soil dries out, soil-water suction increases and causes the water to flow out of it through the porous cup.
  •  The small pores of the saturated cup prevent air from entering it. This outflow of water creates a vacuum inside, and increases the vacuum gauge reading.
  •  If the soil is rewatered through irrigation, the water will be pumped back into the tensiometer, reducing the vacuum inside, and the gauge reading will decrease.

Where Should Tensiometers be Installed?

Tensiometers should be installed in sites that represent the soil types and growing conditions in the area. If the types of soil vary significantly in the area, separate tensiometers should be installed in each of the soil types. Soil humidity should also be taken into consideration during installation. Fields often have wet areas and dry areas, and there are areas that are more wet or dry than the rest of the field. Tensiometers should be placed so as to monitor these areas in order to prevent yield loss.

If two different crops are planted in the same field, install at least one tensiometer for each crop. They should be placed in the wetting zone of the irrigation system. For vegetables growing in beds with drip irrigation, the tensiometer should be installed in the wet zone of the drip strip. It is very important to remove grass, weeds or other obstructions from the ground surface in which the tensiometers are installed.

When Should Readings be Taken?

  • Tensiometer readings should be taken at the same time every day, ideally in the early morning hours before irrigation.
  •  Document the readings. Afterwards, you must interpret tensiometer readings in order to time vegetable irrigation in the soils.
  •  This way you will know whether to stop the irrigation in order to prevent the wasting of water and the washing away of nutrients from the around the roots, you will know if you need to water crops, and you will see if plants display symptoms of water tension, in which case you will need to immediately irrigate.

Tensiometer Maintenance Tips

Please note that in order to provide accurate readings of soil water status during the growing season you must fill all the tensiometers with clean water from time to time, especially following long periods without irrigation or rain. Conduct weekly examinations in order to ensure that they have not been drained and are working properly, examine water levels and examine the proper suction functioning of the vacuum extractor.

We are happy to be at your service with any questions!

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