Using Time Domain Reflectometry to Measure Frost Depth and Unfrozen Water Content in Soil

摘要

Field research using the technique of time domain reflectometry (TDR) was conducted from December 1984 to March 1985 to monitor unfrozen water content and frost depth in soils under the following conditions: vertical steel TDR probes were in continuous, long-term use with relatively long transmission cables, and TDR probes used to monitor unfrozen water content and frost depth in soils seeded to winter wheat and having the following surface management and tillage practices: (1) conventional tillage with a moldboard plot, (2) no tillage with fall seeding using a no-till drill, and (3) bare-surface, continuous fallow tillage. TDR calibration curves relating soil volumetric water content to apparent dielectric constant of the unfrozen soil water were used to compute unfrozen volumetric water content in each of the plots during each of several freeze-thaw episodes. During periods of surface thawing, measurements of unfrozen water content increased as ice melted. A comparison of soil temperature measurements showed that the insulating effect of straw residue at the soil surface in the no-till plot not only prevented deep frost penetration and produced relatively wet soil surface conditions during December and January, it also retarded soil warming compared to the fallow and moldboard plowed plots in February and March.