Open AccessNew Polymer Tensiometers: Measuring Matric Pressures Down to the Wilting Point
Author(s) -
Bakker Gerben,
Ploeg Martine J.,
Rooij Gerrit H.,
Hoogendam Cornelis W.,
Gooren Hermanus P. A.,
Huiskes Cindy,
Koopal Luuk K.,
Kruidhof Henk
Publication year - 2007
Publication title -
vadose zone journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.036
H-Index - 81
ISSN - 1539-1663
DOI - 10.2136/vzj2006.0110
Subject(s) - water potential , permanent wilting point , loam , soil water , polymer , materials science , geotechnical engineering , environmental science , soil science , chemistry , composite material , field capacity , geology
Tensiometers are commonly used for measuring soil water matric pressures. Unfortunately, the water‐filled reservoir of conventional tensiometers limits their applicability to soil water matric pressures above approximately −0.085 MPa. Tensiometers filled with a polymer solution instead of water are able to measure a larger range of soil water matric pressures. We designed and constructed six prototype polymer tensiometers (previously called osmotic tensiometers) consisting of a wide‐range pressure transducer with a temperature sensor, a stainless steel casing, and a ceramic plate with a membrane preventing polymer leakage. A polymer chamber (0.1–2.2 cm 3 ) was located between the pressure transducer and the plate. We tested the polymer tensiometers for long‐term operation, the effects of temperature, response times, and performance in a repacked sandy loam under laboratory conditions. Several months of continuous operation caused a gradual drop in the osmotic pressure, for which we developed a suitable correction. The osmotic potential of polymer solutions is temperature dependent, and requires calibration before installation. The response times to sudden and gradual changes in ambient temperature were found to be affected by polymer chamber height and polymer type. Practically useful response times (<0.2 d) are feasible, particularly for chambers shorter than 0.20 cm. We demonstrated the ability of the instrument to measure the range of soil water pressures in which plant roots are able to take up water (from 0 to −1.6 MPa), to regain pressure without user interference and to function properly for time periods of up to 1 yr.