Tensiometer (soil science)

Tensiometers are used for the continuous measurement of soil moisture based on the soil water potential. The drier is a floor, the greater is the potential of adsorption and capillary forces which bind the water in the soil. Tensiometer type of construction can capture suctions from 0 to about -850 hPa.

Principle of measurement

Soil moisture is the soil water potential, ie the dehydration of a soil is measured. The measurement is performed by means of a water-filled, hermetically sealed, porous ceramic cell ( " ceramic plug" ) (1) with maximum pore diameters of about 1 micron, which is placed in the ground. To check the oil level is a transparent plastic tube ( 2). For the filling of degassed water is used, which may also be colored if necessary.

When the soil dries around the ceramic cell is "pulled" out of the ceramic cell as much water, up to an equilibrium with the surrounding ground water is reached. The resulting vacuum is indicated by a manometer or can be further processed electronically by a pressure sensor (4).

Applications

In soil physical investigations of the water regime in the soil can be continuously measured by tensiometers at various depths. In agriculture and horticulture tensiometers are used in the automation of irrigation systems. Here, the amount of water can be controlled so that the plants are well supplied with water, without water and nutrients are flushed into the ground.

Benefits

The measurement is independent of the salt concentration ( for example, fertilizer salts) in the soil or plant substrate and directly measures the availability of soil water for the plants at the site. The method is not directly dependent on the soil conditions, temperature and other variables - also independent of the absolute amount of water - and thus provides a good measure for the automatic control of irrigation systems.

Disadvantages

Tensiometers measure only selectively. Soil moisture can assume quite different values ​​at a different depth, or in a few centimeters away. Thus, choosing a representative measurement location is crucial. If necessary, water needs to be refilled with tensiometers. This is especially true for measurements in dry soils or substrates. For outdoor use year-round measurements are only possible in Frostproof depth or with the addition of substances such as polyethylene glycol ( PEG).

Another limitation lies in the limited range of tensiometers with water filling. To extend the measuring range therefore osmotic tensiometer can be used with semi-permeable membrane and PEG as a filling.