Abstract
In this paper, soil water movement in layered soilcaused by evaporation from the surface is reported. Three kinds of test columns (the top layer soil only; the top layer soil and sand; the top layer soil, sand and the kuroboku) were placed in chambers which were kept at 20°C, 65% RH or 27°C-32°C, RH free. And the weight of the test columns soil moisture distribution were measured with the lapse of time.
The results obtained are as follows.(1) Specific cumulative evaporation rate curve remains the same without regard to the presence of sublayers.(2) In the initial stage of drying, the average water content of the top layer remains the same without regard to the presence of sublayers, but in the falling rate stage the average water content of the top layer in the test columns having sublayers is larger than that in the columns with no sublayers.(3) Water movement from sand to the top layer begins when the average water content is reduced to 30% and its rate isabout 1/3 of evaporation rate.(4) Soil water in the sand layer moves downward when the average water content of the surface layer is larger than 30%, and moves upward when smaller than 30%.(5) The value of 30% equals the value of the lst critical average moisture content.
