A more precise method employs tensiometers, a sealed, water-filled tube with a vacuum gauge on the upper end and a porous ceramic tip on the lower end. The tensiometer is installed in the seedbed at a depth where the majority of the roots are located. A 12-inch depth is commonly used for surface irrigation, except where a hardpan exists, and there it is placed just above this layer. Shallower settings at about 8 inches deep are recommended for center pivots. Two or three tensiometers per field are recommended to avoid a problem if one of the tensiometers quits working.
Tensiometers are fairly reliable and effective when checked and maintained properly.
However, the time and effort required usually results in most producers not being able to use them very effectively. Soil moisture accounting is used to calculate the soil-water balance in the root zone throughout the growing season. This method is sometimes called checkbook irrigation scheduling because a record is kept on the water that enters and leaves the soil like an account balance is maintained in a checkbook. Two forms of the checkbook procedure are available through county Extension offices in Arkansas the Checkbook User s Guide and the Irrigation Scheduling Computer Program. The Checkbook User s Guide is used to keep a written record of the soil moisture balance when a computer is not available.