Sulfuric Acid Effects on Water Infiltration and Chemical Properties of Alkaline Soils and Water

Abstract

ABSTRACT SULFURIC acid (H2SO4) is a potentially effective amendment for treating alkaline irrigation water and calcareous sodic soils. However, the chemical reactions involved and resulting effects on water infiltration are not fully understood. This subject is reviewed and analyzed when acid is applied to alkaline irrigation water, ammoniated water, and Na-affected calcareous soils. When injected into a closed water system such as sprinkler lines, acid converts HCOj(and C03= if present) to carbonic acid, and reduces the pH of the water below 7 at acid application rates less than equivalent concentrations of HCO^. Upon sprinkling, the accumulated carbonic acid decomposes to CO2, thus leading to Ca precipitation and limited effects on sodicity and water infiltration. When applied to open-ditch flow, acid removes HCO^and CO^^, prevents Ca precipitation at pH above neutral, and may solubilize Ca from soil carbonates. Resulting effects are to maintain or reduce sodicity and to increase electrolyte concentrations, all of which contribute to increasing infiltration of sodic irrigation waters. Water-run application of NH3, a common post-planting fertilization method in row crops, causes severe precipitation of Ca and induces sodium hazards. Acid applied to such water neutralizes alkalinity and minimizes or prevents Ca precipitation and associated infiltration reduction. Acid applied directly to calcarious sodic soils solubilizes CaC03, and at acidic pH releases P, Fe and Al, all of which help increase water infiltration. The amount of exchangeable Na removed by acid is approximately equal to that removed by the chemically equivalent rates of gypsum in moderately Na-affected soils. The closed system reaction under which one mole of H2SO4 potentially releases two moles of Ca would not occur in ordinary reclamation practices. Acid provides faster movement of leaching water than does the chemically equivalent rate of gypsum in severely Na-affected calcareous soils. When applied to moderately Na-affected soils, acid can provide faster leaching than CaCl2 applied at chemically equivalent rates. The effectiveness of acid as an amendment to improve water infiltration depends largely upon chemical properties of soils and water, and application methods.