Field Tensiometers
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| 25.01.2010 | Author: sathya | Posted in Soil Plant and Water Relation | | Print
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Field-installed tensiometers are generally equipped with pressure gauges or mercury manometers. These read-out devices require much maintenance, while the cost of gauges is high when used in large quantities. Tensiometers are useful instruments for measuring soil water status in the field. Tensiometers measure soil water potential or tension, which is a measure of the amount of energy required for a plant to overcome capillary and gravitational forces to extract water from a soil. Thus, tensiometers can be used to schedule irrigations when the soil water tension is low — that is, before plant water stress occurs. Tensiometers do not measure the osmotic component of soil water potential, which is due to soil salinity. However, this would not be expected to be a limitation to the use of tensiometers in Florida except in saline soils or where saline irrigation water is used.
A tensiometer is a water-filled tube with a vacuum gauge and filling port at the upper end and a ceramic cup at the lower end. When it is placed in the soil, the water in the instrument comes to equilibrium with the water in the soil by flowing through the ceramic cup. At equilibrium, the water tension in the instrument is equal to the water tension in the soil. Then the vacuum gauge measures the soil water tension.
A tensiometer is used by placing it in the field so that the ceramic cup is located within the root zone of the plants to be irrigated. Then the instrument measures the soil water tension that the plants are experiencing.
The tensiometer is a fairly simple instrument that will work well if it is properly installed and in good condition. The instrument is in good repair if:
1) The vacuum gauge is accurate.
2) The ceramic cup allows free water movement between the soil and the instrument.
3) There are no air leaks.
TENSIOMETER CALIBRATION
. Calibration is periodically required when tensiometers are used to control irrigation scheduling, especially for crops that are very sensitive to water stress. Two calibrations can be performed:
1) The vacuum test gauge quick calibration.
2) The vacuum chamber detailed calibration.
