EFFECTS OF IRRIGATION WATER COMPOSITION ON EXCHANGEABLE SODIUM STATUS OF A FIELD SOIL

A Valencia orange orchard cultivated on Greenfield sandy loam was basin irrigated with uniform amounts of each of four waters for 8 years. The leaching fraction (LF) management was held at 0.15 for each of the irrigation treatments. Water composition was such that the water used had a range in salinity and potential sodicity hazard from low to moderate (ECiw, 0.5 to 2.5 mmho/cm; SARiw, 1.1 to 3.7; and pHc, 6.8 to 7.5). The differently irrigated plots were sampled by horizons each year and analyzed for exchangeable sodium. Maximum ESP values were attained after 3 years of treatment. Equilibrium ESP values for the 0.0–0.3-m horizon ranged from 2.1 to 4.4, depending upon the irrigation water applied. Calculated ESP values, taking into consideration SARiw, the precipitation and dissolution of soil minerals, and LF management were markedly higher than the observed ESP values. The differences between the observed and estimated ESP values were attributed primarily to an overcorrection for alkaline earth carbonate precipitation by the conventional pHcadjustment. © 1979 The Williams & Wilkins Co.