Water availability in the soil has a strong influence on the vitality and growth of plants. It is recorded with tensiometers.
These measure the suction tension, i.e., the force with which water is retained in the pores between the soil particles. A plant must overcome this force in order to absorb soil water via its roots. These data show how soil texture but also extreme weather events and climate change affect water availability for plants.
The tensiometer consists of a tube filled with water. We measure the vacuum (negative pressure) that builds up in the tube when water is "pulled" out of the tube into the ground. The tensiometers are installed in three to five depths between 15 and 130 cm. We retrieve the data manually every 14 days.
The seasonal development of the suction tension varies from region to region. On the Swiss Plateau, there are often one or more dry episodes between June and October.
In the heat summers of 2003, 2015 and 2018, the soil dried out to such an extent that measurement with tensiometers was no longer possible (measuring range between 0 and -850 hPa). In contrast, the soils of LWF sites at higher altitudes (above 1200 m) hardly ever dry out in the summer.