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The Soil tensiometer is designed to be the most economical tensiometer commercially available. It is manufactured in France, and is used extensively throughout France and Europe. Its simple construction and Bourdon-tube gauge make it an inexpensive yet accurate and reliable instrument.

Tensiometers are simple, reliable instruments which provide a measure of the moisture status of the soil. They have been in use for many years, and due to their simple design and rugged construction, continue to be the standard instrument for tension measurement.

Tensiometers help answer the irrigators' questions of when and how much irrigation water to apply. Maintaining proper moisture conditions is necessary for achieving optimal plant growth and quality. Monitoring the moisture status of the soil allows for timely and efficient irrigations, and for avoiding unnecessary irrigations.
 

Features

• direct measurement of moisture conditions
• no calibration required
• Large inner-diameter body tube and water reservoir

How they are used

rs the active root area and is used to determine when an irrigation is needed. A second tensiometer, installed near the bottom of the root zone, is used to adjust the irrigation amount or system run-time in order to ensure that sufficient water is being applied, and to avoid over-irrigation and loss of water and chemical amendments due to drainage beyond the root zone. The moisture status of the soil is monitored by reading the tensiometers periodically. When the tension readings in the upper tensiometer reach a certain level, an irrigation is needed. This tension level is determined by the irrigator, and depends upon such factors as crop type, soil condition, and root depth. The lower tensiometer is monitored to ensure that enough water has been applied to refill the root zone.

What the readings mean

Tensiometers measure the tension with which water is held in the soil. A plant root must overcome this tension in order to extract water held onto the soil particles, and to take in water and nutrients. Low tension readings indicate moist conditions, with water readily available and easy for the plants to extract. As the soil dries, the remaining water is held more tightly to the soil. Tension readings increase, and plant roots have more difficulty extracting water and maintaining optimal growth. At some point, irrigation becomes necessary to maintain growth and quality, and to avoid plant damage.

When to irrigate

Factors such as plant variety, soil texture, and growth stage determine the tension at which irrigation should commence. Some examples of recommended tension readings at which to begin irrigation are shown in the following table, with information for other crop types found in the Installation and maintenance.

Tensiometers are simple to install and use. A soil auger is used to make the proper-sized hole in the ground. The tensiometer is then inserted into the hole and left permanently. Periodically, the tensiometer may need to be refilled with water. Under irrigated conditions, however, the tensiometer will usually refill itself when irrigation water is applied to the field.

Interpreting readings

 Tension readings are often used to determine when an irrigation is needed.  The grower establishes a critical level of moisture depletion which will be allowed, beyond which vegetative growth or fruit quality are affected.  As the soil dries, tensiometer readings increase in response to roots having to pull harder to extract water from the soil.  When the readings approach the critical moisture level, the irrigation point, an irrigation is needed.