Abstract
In a snowy and cold area of northern Japan, heat fl uxes on soil surface were investigated in several plastic greenhouses with different crop and cultivation conditions. The results can be summarized as follows:
(1) The daily changes in heat fl ux on soil surface depended on the kind of growing crops under the similar conditions of solar radiation. In a plastic greenhouse which fl oor was always covered by the leaves and stems of hydroponically grown rose plants, upward heat fl ux on soil surface was less than 5 W m-2, and smaller than those for other crops. On the other hand, in the plastic greenhouse which cultivated cucumber or cherry plants, the solar radiation was accumulated into the soil, and the upward heat flux in the nighttime was about 20 W m-2 or less.
(2) The changes in heat fl ux on soil surface during the investigation period depended on the plant growth stage, too. Although the solar radiation increased after March, the heat fl uxes on soil surface did not increase. The amount of solar radiation reaching onto soil surface was decreased by an increase in leaf area.
