Development of Tensiometer for Monitoring Soil-Water Dynamics in a Freezing and Snow Covered Environment

Abstract

A thermally insulated tensiometer was developed to investigate the water movement under frozen soils at a study site in the central part of the Tokachi Plain which is one of the largest agricultural areas of seasonally frozen soil in Japan. The above- and below-ground parts of tensiometers, which are susceptible to freezing, were housed in a thermally insulated chamber with a small internal heat source (a 5-W incandescent light bulb). The matric potentials below frozen layer were monitored using the tensiometers with other soil and meteorological parameters in the winter of 2001-2002 and 2002-2003. The data indicated that tensiometers for long-term monitoring of matric potential under frozen soil in a snow covered environment should have; (i) a sufficiently large water reservoir, (ii) the bottom half of the heated chamber buried to keep it from rising with frost heave, (iii) a relatively low-power incandescent light bulb and sufficient distance between the heated chamber and porous cups to reduce the influence of the chamber on soil temperature and water potential. Taking these into account, a new tensiometer was designed and used in the winter of 2003-2004, resulting in significantly improved data quality.