A tensiometer

A gauge face showing centibar graduations

Top, making hole slightly smaller than tensiometer shaft diameter for a snug fit; middle, filling the hole with water; bottom, inserting the tensiometer, making sure it is well seated. Do not use excessive force.

Soil tension levels used to schedule irrigation vary with soil texture. In a sandy loam, irrigation should begin when soil tension reaches 20 centibars (a unit of pressure) and cease when it falls to 10 centibars. A soil tension reading of 0 indicates complete saturation. In a finer-textured soil such as silt loam, there is no need to irrigate until soil tension reaches 30 centibars.

Insert the tensiometer as you would a probe, 6 to 12 inches from the base of the plant or in the row if crops are closely spaced.

Expect to spend extra time at first to learn how the tensiometer reacts to various weather and cropping situations. With time, you will be able to schedule irrigations to achieve the desired soil moisture response.

Tensiometers come in various lengths. The 6-inch model is ideal for use in raised beds. Although not required, a 12-inch model placed alongside the 6-inch tensiometer helps determine the depth of water penetration so that water won't be wasted.

Because of their cost ($50 to $60 for a 6-inch model), it is impractical to place a tensiometer in every bed or crop. If you have only one tensiometer, locate it among plants having the greatest water demand (tomatoes would be the candidate in most gardens). Adjust irrigation to match water requirements of other crops accordingly.

For information on the use and care of your tensiometer, refer to the owner's manual. With proper care, a tensiometer can provide many years of useful service. For a list of tensiometer (also called an irrometer) merchandisers, refer to the appendix.

Following these guidelines will help you manage your water resource. Proper scheduling of irrigation will help ensure maximum production with minimum watering.