Comparison of soil frost depth and its duration determined by soil frost tube and soil temperature interpolation

Abstract

Soil frost and the depth of freezing are important for the plant developmentand for the building industry as well. The depth of soil frost is estimated directly by soilfrost tube and indirectly from diagrams of soil temperature according to the isotherm of0 °C (zero-isotherm). The soil temperature measurement is often used for evaluation offreezing depth, because the frost tubes measurement is rarely performed. Measurementby frost tube is done once a day at 7 a.m. and soil temperature in 5, 10, 20, 50 and100 cm is measured in three observation terms at 7 a.m., 2 p.m. and 9 p.m. Data fromagroclimatological station Pohořelice (1971–2000) were used for the evaluation. Threespecific real cold periods (1978–1979, 1984–1985 and 1990–1991) and mean frost depthand absolute maximal frost depth for the whole period were evaluated. Course of frost,terms of beginning and the end of frost period and the term of maximum freezing assessedby both methods are almost identical in all real evaluated periods. The results show thatthe soil frost depth measured by soil frost tube is often higher than that estimated from soiltemperature diagrams. It might be caused by graphical processing, as soil temperaturesare measured only at five given depths and the depth of zero isotherm is determined bytheir interpolation. The most significant differences between both methods were observedwhen evaluating average values for the entire period 1971–2000.