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Water Content Changes Following Irrigation of Bare-Field Soil That is Protected from Evaporation¹

ABSTRACT

Water content changes were measured in a field plot of sandy loam soil. Following basin irrigation with 35 cm. of water, the soil surface was sealed with a sheet of polyethylene and covered with 10 cm. of straw. The measurements were made over a 50-day interval during the summer of 1955. It was found for this soil that the water content, W_D, expressed in surface cm. of water in a surface layer of soil of depth D cm. could be closely related to the time T in days following irrigation by W_D = (0.52 + 0.209 D + 0.00053 D²) T^-0.128. The downward flow rate dW_D/dT = v_D, expressed in cubic cm. per sq. cm. per day, as related to depth, and time is obtained by differentiation of the water content equation. Hydraulic head values in the field soil were measured. The capillary conductivity values calculated from the field data were found to be in agreement with values obtained previously by both laboratory and field methods for this soil.

¹ Contribution from the U. S. Salinity Laboratory, Soil and Water Conservation Research Branch, A.R.S., U.S.D.A., Riverside, Calif., in cooperation with the 17 Western States and the territory of Hawaii.

² Soil Scientist and Physicist, respectively.

Received for publication June 4, 1956. Accepted for publication March 29, 1957.