Soil moisture

A soil is saturated with water, when all the pores of the soil with water are filled. Part of this soil water penetrates into deeper zones as seepage water , while another part, the adhesive water , which is held in the soil against gravity , forms the actual soil moisture .

Classification

In soil science, soil moisture is divided into the following stages: wet, moist, fresh, dry and arid .

• A wet soil is so low above the groundwater that the soil moisture runs off when the soil is lifted out. After heavy rainfall , the water accumulates.
• A damp soil releases water when it is compressed.
• A fresh soil has a moderate water content that does not run off when compressed.
• A dry soil has no noticeable, liquid water.
• A sandy soil is usually referred to as dry soil , the individual grains of which hardly show any moisture.

Extreme values

The maximum value of the soil moisture is defined as the field capacity , this is the amount of water that a soil completely saturated with water can still hold after two to three days of drainage under standardized conditions. In most soils this corresponds to a suction tension of −60  hPa to −300 hPa.

The minimum extreme value of soil moisture for plants is at the permanent wilting point (PWP), at which sunflowers (Helianthus annuus) and pines (Pinus sylvestris) , even with good rooting, can no longer withdraw enough water from the soil and wither irreversibly . It is usually applied at a suction stress of −1.5 MPa (or pF value 4.2).

The water conductivity of the soil is so low at the permanent wilting point that the transpiration losses of the plant can no longer be compensated. The pore volume of the soil is drained in the area of ​​the coarse and medium pores. The remaining part of the soil moisture that can no longer be used by the plants is also known as dead water .

Measurement methods

• Capacitive moisture meter
• Impedance spectroscopy
• Humidity measurement with time domain reflectometry
• Tensiometer
• Cooling time after the sensor has heated up ( thermal conductivity )

See also

• Water capacity
• Material moisture
• Water content
• Water potential

literature

• Karl Heinrich Hartge : Introduction to Soil Physics. Enke, Stuttgart 1978, ISBN 3-432-89681-6 , pp. 212-216.
• Deming Zhao, Claudia Kuenzer, Congbin Fu, Wolfgang Wagner: Evaluation of the ERS Scatterometer-Derived Soil Water Index to Monitor Water Availability and Precipitation Distribution at Three Different Scales in China. In: Journal of Hydrometeorology. Vol. 9, No. 3, 2008, ISSN  1525-755X , pp. 549-562, doi : 10.1175 / 2007JHM965.1 .

Individual evidence

1. ↑ What is “fresh ground”? Weekly newspaper for agriculture & rural life , August 4, 2010.
2. ↑ Emil Ramann : Soil Science. Springer, Berlin 1911, p. 356.
3. ↑ Andrey Tetyuev: Bodenartunabhängige soil moisture measurement by means of impedance spectroscopy. Dr. Hut, Munich 2009, ISBN 978-3-86853-206-7 (also: Chemnitz, Technical University, dissertation, 2009).