RETENTION OF ANHYDROUS AMMONIA BY SOIL

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Abstract
Ammonia retention by soils, as influenced by NH3 concentration and moisture content, was characterized by studying the rate and extent of NH3 desorption from ammoniated soils by a continuous aeration procedure. Tne rate of desorption was found to be an increasing function of the NH3 concentration applied. Characteristic thresnold concentrations were observed for two soils below wnich the initial rate of NH3 desorption decreased markedly. Rate of NH3 desorption is probably governed mainly by the strengths of the various NH3-absorbent bonds. Wnen soils were treated with progressively higher NH3 concentrations a point was reached where only very small additional increments of NH3 were ultimately retained. Tne retention mechanism(s) responsible for this phenomenon appears to be concentration dependent and may have involved certain higner-order reactions, or tne formation of coordination complexes of NH3. In a study of the effect of soil moisture on the rate and extent of NH3 desorption from ammoniated soils, it was observed that: (a) desorption rate during the early period of aeration was inversely related to the moisture level, and (b) more NH3 was ultimately retained by tne air-dry and oven-dry soils tnan by tne moist systems, which suggests a possible competitive interaction between NH3 and water. Further evidence of this interaction was oDserved when a considerable fraction of the NH3 retained by an oven-dry soil was rapidly displaced Dy water vapor from a moist air stream. Competition Detween NH3 and water for sorption and reaction sites in a soil is apparent only when relatively small amounts of water are present. Any interaction Detween these two molecules is probably masked when water is present in sufficient quantity to act as a solvent for NH3.

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