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Ammonia Losses from Surface-Applied Urea and Ammonium Fertilizers as Influenced by Rate of Soluble Calcium¹

ABSTRACT

Previous research has shown that applying large amounts of soluble Ca with urea and NH₄ fertilizers depressed ammonia (NH₃) losses extensively. This paper reports effects of varying amounts of Ca on reduction of this loss. Ammonia loss was progressively less with increasing Ca/N ratios. In the greenhouse, a Ca/urea-N equivalent ratio of 0.25 reduced NH₃ losses to 11% of applied N. In the laboratory, this ratio reduced NH₃-N losses to 42% of applied N; without Ca, N losses were 75%.

Soluble Ca was effective in reducing NH₃ losses from urea when surface applied to both acid and calcareous soils. Increased acidity from the application of soluble Ca salts on acid soils reduced the amount required to reduce NH₃ losses. Soluble Ca applied with (NH₄)₂SO₄ (AS) and NH₄NO₃ (AN) also reduces NH₃ losses from calcareous soils. Reduction of NH₃ losses from AN was due solely to lowered soil pH values. However, reduction of NH₃ loss from urea and AS was possibly due both to CaCO₃ precipitation and soil pH depression.

¹ Contribution from Texas Agric. Exp. Stn., Texas A&M Univ., College Station, TX 77843.

² The first and the last Authors are Associate Professor and Laboratory Technician, respectively, Texas A&M Univ. Res. Center, 1380 A&M Circle, El Paso, TX 79927; the second Author is Professor, Texas A&M Univ. Res. and Ext. Center, P.O. Box 10607, Corpus Christi, TX 78406.

Received for publication October 23, 1978. Accepted for publication February 26, 1979.