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Sulfuric Acid for the Treatment of Ammoniated Irrigation Water: II. Reducing Calcium Precipitation and Sodium Hazard¹

ABSTRACT

Effects of ammonia (NH₃ or NH₄OH) and sulfuric acid (H₂SO₄) applied to ammoniated water on Ca precipitation and Na-hazard of irrigation water are evaluated theoretically using known relations of ion equilibria and tested with laboratory and greenhouse experiments. Results show a severe precipitation of Ca²⁺ when ammonia is applied to alkaline irrigation waters. At ammonia rates ranging from 25 to 100 mg/liter, for instance, 80 to 95% of Ca²⁺ present in water may precipitate as CaCO₃ even under a closed system. Ammonia application also increases exchangeable Na and NH₄, and can reduce water infiltration rates, especially when irrigation waters contain high Na⁺ relative to Mg²⁺ and Ca²⁺. Sulfuric acid applied to ammoniated water neutralizes OH^- produced by ammonia application. Thus it reduces Ca precipitation and exchangeable Na, and consequently prevents a decline in infiltration rates. Sulfuric acid, which is now available as a pollution abatement byproduct in the Southwest, can be used for correcting excessive lime incrustation or poor water penetration induced by the use of anhydrous or aqua ammonia without corroding irrigation systems.

¹ Arizona Agric. Exp. Stn. No. 2503. Contribution from the Dep. of Soils, Water, & Engineering, The Univ. of Arizona, Tucson 85721. Supported in part by a grant from the Arizona Mining Assoc.

² Associates in Research. The senior author is currently at Dep. of Agronomy, New Mex. S. Univ., Las Cruses, NM 88003 and the junior author is at Dep. of Soils & Irrigation, Am. Univ. of Beirut, Lebanon.