Abstract
Soil frost and the depth of freezing are important for the plant development
and for the building industry as well. The depth of soil frost is estimated directly by soil
frost tube and indirectly from diagrams of soil temperature according to the isotherm of
0 °C (zero-isotherm). The soil temperature measurement is often used for evaluation of
freezing depth, because the frost tubes measurement is rarely performed. Measurement
by frost tube is done once a day at 7 a.m. and soil temperature in 5, 10, 20, 50 and
100 cm is measured in three observation terms at 7 a.m., 2 p.m. and 9 p.m. Data from
agroclimatological station Pohořelice (1971–2000) were used for the evaluation. Three
specific real cold periods (1978–1979, 1984–1985 and 1990–1991) and mean frost depth
and 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 assessed
by both methods are almost identical in all real evaluated periods. The results show that
the soil frost depth measured by soil frost tube is often higher than that estimated from soil
temperature diagrams. It might be caused by graphical processing, as soil temperatures
are measured only at five given depths and the depth of zero isotherm is determined by
their interpolation. The most significant differences between both methods were observed
when evaluating average values for the entire period 1971–2000.