THE EFFECT OF SOIL SUCTION ON EVAPORATIVE FLUXES FROM SOIL SURFACES

This paper presents a theoretical approach in which a Dalton-type mass transfer equation is used to predict the evaporative fluxes from nonv egetated soil surfaces. Soil evaporation tests were conducted in the l aboratory on three different soil samples of Beaver Creek sand, Custom silt, and Regina clay. The soil surfaces were saturated and allowed t o evaporate to a completely air-dried state. The actual evaporation ra te for each soil surface was measured along with the potential evapora tion rate for an adjacent water surface. The ratio of actual evaporati on to potential evaporation or normalized soil evaporation was then ev aluated with respect to drying time, soil-water content, and soil suct ion. The value of the normalized soil evaporation was found to be appr oximately equal to unity for all soils until the total suction in the soil surfaces reached approximately 3000 kPa. The rate of actual soil evaporation was observed to decline when the total suction exceeded 30 00 kPa. A relationship between the actual evaporation rate and total s uction was found to exist for all three soil types which appears to be unique and independent of soil texture, drying time, and water conten t.