EVAPOTRANSPIRATION IN CRACKED CLAY FIELD SOIL

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Evaporation from shrinkage cracks which had developed vertically in a clayey field soil was determined by investigating the distribution of the temperature and humidity in the cracks. Evaporation from the whole soil surface including the cracks and evapotranspiration were also determined by the calculation of the heat balance. The results obtained are summarized as follows: 1) Evaporation from the whole soil surface accounted for 2-12% of the evapotranspiration. Evaporation from the cracks alone accounted for 10-50% of the evaporation from the whole soil surface, although the area of cracks accounted for only about 6.7% of the soil surface area. These findings suggest that cracks may intensify the water loss from bare soil. 2) The direction of the water vapour flux in vertical cracks was downward from a depth of 7.5 cm and upward at the soil surface during the daytime on a fine day. At a depth of 3 cm, the water vapour flux in the cracks changed from a downward to an upward direction with the drying of the soil. The horizon at a depth of about 0-5 cm, therefore, is likely to lose soil water, but the horizon below about 5 cm is likely to enrich the water vapour in the cracks. 3) The movement of the water vapour in the cracks described above was associated with the rapid rise of the temperature in the upper portion of the cracks which caused a considerable increase of the water vapour density. Consequently, the gradient of the water vapour density was divided into upward and downward directions at the depth of the boundary with the zone with the highest water vapour density. These observations suggest that a rapid increase of temperature creates a barrier that prevents evaporation from cracks.
社団法人日本土壌肥料学会の論文

EVAPOTRANSPIRATION IN CRACKED CLAY FIELD SOIL

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