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Infiltration, Redistribution, and Subsequent Evaporation of Water from Soil as Affected by Wetting Rate and Hysteresis¹

ABSTRACT

Soil columns were wetted at three different rates which caused unequal water content profiles during infiltration. Water content profiles during infiltration, redistribution, and evaporation were observed experimentally and computed using a numerical solution of the isothermal flow equation. Each wetting rate resulted in a different drying water retention curve. The hysteresis in soil water content-water suction relationships had a larger influence as the wetting rate increased. Hysteresis effects tend to keep the water content higher and the zone of wetting shallower during the redistribution stage when rates of wetting are faster. Higher water content and lower wetting depth at any redistribution time caused subsequent evaporation to be greater. Evaporation was directly related to the previous wetting rate, either when the soil was subjected to evaporation immediately following infiltration or when subjected to evaporation after redistribution for 4 days. The differences in evaporation between the three wetting treatments were significant at the 99% probability level. Allowing time for redistribution decreased evaporation compared to evaporation and redistribution occurring simultaneously. The effects of wetting rates and hysteresis on water content profiles and evaporation were similar in the experimental and computed results.

¹ Contribution from the Department of Agronomy, Colorado State Univ., Fort Collins, and the Northern Plains Branch, Soil and Water Conservation Research Division, ARS, USDA, Ft. Collins, Colo. Published with the approval of the Director of the Colorado Agr. Exp. Sta. as Scientific Series Paper no. 1397. This work was supported in part by the Department of Interior, Office of Water Resources Research, under P. L. 88–379.

² Temporary Assistant Professor and Soil Scientist, USDA; Professor of Soil Science, Colorado State University, Ft. Collins; and Professor of Soils & Meteorology, Utah State University, Logan. The senior author is now at the Volcani Institute of Agricultural Research, Rehovot, Israel.

Received for publication March 13, 1969. Accepted for publication July 31, 1969.