Summary: This paper presents the results of temperature measurements made in Kopáncs in the South of Hungary (46° 20' N) in the course of microclimatic research. In the present first part the temperature of the sodic soil, the 20 cm water layer and the soil under it, as well as of the 20 cm flooding-water of the paddy stand and the soil under it is described.

The paddy fields of Kopáncs create a peculiar local climate in the vegetation period. The author shows the diurnal variation of the heat flux in the soil separating the divergence and convergence levels. These are the inversion levels of the soil. The layer of soil in which there are inversion levels is the daily inversion layer of the soil. There are inversion levels also in the soil covered by water. The sinking of the inversion levels depends not only on the properties of the soil but also on the weather.

On the basis of temperature measurements taken hourly at 2, 5, 10, 15, 20, 25 and 30 cm in sodic soil the times of the occurrence of the maxima and minima, the phase lag and the duration of solar radiation, and with reference to cloudiness, the daily soil temperature amplitudes are discussed.

Soil temperature was measured at 0, 2, 5, 10 and 20 cm in the soil under open water and under the flooding- water of the paddy. It is seen from these investigations that in the soil under water the extreme temperatures have a phase lag of 4–5 hours as compared to the soil not covered by water, and an additional 1 hour lag in the soil of the paddy. The daily temperature variations are also more moderate in the soils under water. Owing to the growth of the mass of the paddy stand the daily temperature variations of its soil become smaller in the phenophases, and this decrease may even reach 50% as compared to the temperature variations in the soil under water.

Warming up of the open water layer starts not only from the water surface, but also from the water bottom, and the soil under the water also plays a role in the cooling of the water. The flooding-water of the paddy usually warms up and cools down from the water surface.

Owing to the shade effect of the vegetation, the temperature maxima and minima occur later, and the daily temperature variations are smaller in the flooding-water of the paddy than in the open water.