The purpose of this study was to determine the effect of soil CaCO 3 content on ammonia volatilization from surface applied ammonium compounds. Ammonia‐nitrogen losses from surface‐applied (NH 4 ) 2 SO 4 increased rapidly to 6.1% soil CaCO 3 , with slight NH 3 loss increases from 6.1 to 9.7% soil CaCO 3 , and no NH 3 loss increase beyond 9.7% soil CaCO 3 . Ammonium nitrate reached maximum NH 3 ‐N loss at 1.3% soil CaCO 3 and 110 kg NH 4 + ‐N/ha, with lower but still increasing losses of NH 3 ‐N at 6.1% soil CaCO 3 and 550 kg NH 4 + ‐N/ha. The acidity of the ammonium compounds caused a reduction in final soil pH at low CaCO 3 levels and high NH 4 + ‐N application rates; but at 6.1% soil CaCO 3 and above, the pH values remained at 7.5 to 7.6. The effect of soil pH on NH 3 ‐N losses was greater for NH 4 NO 3 than for (NH 4 ) 2 SO 4 . For (NH 4 ) 2 SO 4 , the percent loss of NH 3 ‐N below 1.3% soil CaCO 3 decreased as NH 4 + ‐N application rates increased; but at 2.9% and above, NH 3 ‐N losses were greatest at the highest rate of NH 4 + ‐N application. In contrast, no reversal in NH 3 ‐N losses were observed for NH 4 NO 3 with increasing soil CaCO 3 content and NH 4 + ‐N application rates. Multiple regression analysis of NH 3 ‐N losses with respect to time, temperature, rate of NH 4 + ‐N application, and soil CaCO 3 content resulted in two equations with correlation coefficients ( R 2 ) of 0.88 and 0.85.
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Fenn et al. (1975) studied this question.