tensiométrie

CONT: Le potentiel matriciel de l'eau du sol. [...] Trois types de mesure sont couramment utilisés : - par extraction de l'eau sous pression [...] - par équilibre hygroscopique [...] - par tensiométrie. Les tensiomètres laissés à demeure dans le sol donnent le potentiel matriciel par simple lecture de la hauteur d'une colonne manométrique. Cette méthode est applicable dans la gamme allant de 0 à -0,1 MPa environ.

CONT: The matric potential h[subscript c] is negative in unsaturated soil (pores partly filled with water and partly with air), because work is needed to withdraw water against the soil matric forces. It is not essential to know these forces in detail: it suffices that h[subscript c] can be measured by tensiometry or other techniques.
CONT: Tensiometry ...: Two kinds of devices are widely distributed on the French market: 'standard' tensiometers (porous cup linked to a depression manometer by a tube filled with water); and watermark sensors (electrical measure block buried in the ground and removable meter). Tensiometers measure the soil matric potential (but only below 100 kPa). A little delicate to implement, exacting to pick out (automation is desirable), nevertheless they are a good tool for controlling the irrigations (particularly drip). Nowadays they are more used by agricultural advisers than by farmers, unless the latter are well trained.