Effect of ammonium fertilizer on NH3 loss and Ca,Mg, ammonium and nitrate content in a calcareous soil solution

Summary This study examined the effects of NH _inf4 ⁺ fertilizers [(NH₄)₂SO₄, (NH₄)₂HPO₄, CO(NH₂)₂, NH₄OH, and NH₄NO₃] on NH₃ loss and the quantity of Ca + Mg, NH _inf4 ⁺ and NO _inf3 ^sup– in the solution of a calcareous soil (Harkey sicl, Typic Torrifluvent). Various NH₄ fertilizers applied at a depth of 5 cm in the soil produced differing NH₃ loss characteristics. Applying (NH₄)₂SO₄ (AS) resulted in high volatile NH₃ losses as compared with NH₄OH (AH) and (NH₄)₂CO₃ (AC). The AS treatment formed an equal molar amount of CaSO₄, which increased the mobility of ammonium, while AH and AC treatments caused Ca precipitation and decreased ammonium mobility. Leaching the AS system before NH₃ loss could occur resulted in the most rapid nitrification rate. Lower nitrification rates were found with AH and AC than AS under the same conditions. Surface placement of NH₄ fertilizers resulted in variable leachate contents of Ca + Mg. Ammonium sulfate reacted with CaCO₃ either to solubilize some Ca + Mg or simply to replace exchangeable Ca + Mg with NH₄, while AH, AC, and (NH₄)₂HPO₄ (DAP) precipitated essentially an equivalent molar amount of soluble and adsorbed Ca + Mg. Use of NH₄NO₃, which does not form an insoluble calcium precipitate, resulted in the leaching of an equivalent molar amount of exchangeable Ca + Mg from the Harkey soil.The authors are Professor and former laboratory technician, respectively, at Texas A&M Research Center at El Paso, 1380 A&M Circle, El Paso, TX 79927, USA