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Ammonia Volatilization from Surface Applications of Ammonium Compounds on Calcareous Soils: IV. Effect of Calcium Carbonate Content¹

ABSTRACT

The 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.

¹ Contribution from Texas Agric. Exp. Sta., Texas A&M University, College Station, Texas 77843.

² Assistant Professor and Associate Professor, Texas Agric. Exp. Sta., located, respectively, at Texas A&M Agric. Res. Center at El Paso, 10601 North Loop Road, El Paso, Texas 79927, and Blackland Conservation Research Center, Box 748, Temple, Texas 76501.

Received for publication September 30, 1974. Accepted for publication March 3, 1975.