Effect of sulfuric acid on sodium-hazard of irrigation water

Abstract

The sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP) and saturated hydraulic conductivity were measured under laboratory conditions in one neutral and four calcareous soils using simulated alkaline irrigation waters having salt concentrations ranging from 7 to 39 meq/l with the SAR from 3.8 to 8.4. Sulfuric acid was applied to the waters at sufficient rates to prevent calcium precipitation under an open system, ranging from 2.1 to 4.7 meq/l. At these acid rates, the pH of irrigation waters remained above neutral. This treatment reduced SAR and ESP in all cases tested, and increased the hydraulic conductivity of some soils when the SAR of the original irrigation waters was greater than approximately 7. The experimentally determined SAR was then compared with the values predicted based on some of the existing theories. The results indicated that the conventional method to estimate SAR with adjustment using the pHC index of Langelier overestimates the effect of HCO3 -, whereas the equation based on carbonate equibria gives a reasonable prediction of SAR in waters containing HCO3 - as well as H2SO4. The SAR calculated by the latter method was also linearly related to the measured ESP with an equation, ESP=0.761 SAR, r2=0.986.