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'0 .-. . . . . conditions can be expressed as a function of the water used.in evapotran- 0' spiration, Wet' and the' concentration 'of salts in'the water. If there is negligible precipitation or solubility of salts in the root zone, a salt balance is maintained and . . C W -CW aw aw d d (2.3) , where Caw is the average concentration of salts in the water applied, Waw is the depth reached by irrigation water and rainfall, Cd is the concentra- tion of salts in the water draining from the root zone, and Wd is the depth of water draining from the root zone. Since Waw = Wet' and by substituting the concentration of salts that can be tolerated near the lower part of the - toot zone near field capacity, the quantity of water required for leaching, WL, can be predicted. by the equation: o . Caw WL .. ELCr - Caw Wet o o (2.4) The leaching efficiency term, EL, has been added to account for the nonuniform removal of salts per unit area. It represents the ratio to the average salt concentration in the root zone near field capacity, EL = Cd/Cr' The concen- tration of salts in equations 2.3 and 2.4 can be represented by its electrical ,conductivity, EC. A more complete description of the leaching concept and the sensitivity of various crops to salts in the soil solution can be found in the following publications: " "Diagnosis and Improvement of Handbook Number 60, Salinity Washington, D.C.~Rev. 1969, Saline and Alkali Soils," Agriculture Lab, U.S, Department of Agric., 160 pp. Wilcox, L. V., "Salt Balance and Leaching Requirement in Irrigated Lands," Technical Bulletin 1290, U.S. Department of Agric., Washington, D.C., 1963, 23 pp. Bernstein, L., "Tolerance of Plants to Salinity," Journal of the Irrigation and Drainage Division, ASCE, ~ol. 87, No. IR4, Proc~ Paper,300S, December, 1961, pp, 1-12. Preliminary soil analysis by USBR of soil samples from the area to ,be irrigated shows 'that the 'conductivity of the saturation extract can be , '.