Ammonia Volatilization from Surface Applications of Ammonium Compounds on Calcareous Soils: IV. Effect of Calcium Carbonate Content

Abstract

AbstractThe purpose of this study was to determine the effect of soil CaCO3 content on ammonia volatilization from surface applied ammonium compounds. Ammonia‐nitrogen losses from surface‐applied (NH4)2SO4 increased rapidly to 6.1% soil CaCO3, with slight NH3 loss increases from 6.1 to 9.7% soil CaCO3, and no NH3 loss increase beyond 9.7% soil CaCO3. Ammonium nitrate reached maximum NH3‐N loss at 1.3% soil CaCO3 and 110 kg NH4+‐N/ha, with lower but still increasing losses of NH3‐N at 6.1% soil CaCO3 and 550 kg NH4+‐N/ha.The acidity of the ammonium compounds caused a reduction in final soil pH at low CaCO3 levels and high NH4+‐N application rates; but at 6.1% soil CaCO3 and above, the pH values remained at 7.5 to 7.6. The effect of soil pH on NH3‐N losses was greater for NH4NO3 than for (NH4)2SO4. For (NH4)2SO4, the percent loss of NH3‐N below 1.3% soil CaCO3 decreased as NH4+‐N application rates increased; but at 2.9% and above, NH3‐N losses were greatest at the highest rate of NH4+‐N application. In contrast, no reversal in NH3‐N losses were observed for NH4NO3 with increasing soil CaCO3 content and NH4+‐N application rates.Multiple regression analysis of NH3‐N losses with respect to time, temperature, rate of NH4+‐N application, and soil CaCO3 content resulted in two equations with correlation coefficients (R2) of 0.88 and 0.85.