Comparative behavior of ammonia and ammonium salts in soils

Abstract does not appear. First page follows.

Introduction

Some years ago anhydrous ammonia (NH₃) was introduced in California as a nitrogen fertilizer. This compound, sold as “Agricultural Ammonia” and “Shell NH₃,” is available in the form of a liquefied gas compressed in strong steel cylinders that weigh about 150 pounds.

Agricultural Ammonia is applied on the land during irrigation. The cylinders are connected to a simple metering device, and the ammonia is released as a gas into the irrigation water. Thus the ammonia is distributed in a very dilute solution (100 to 500 p. p.m.). In water ammonia (NH₃) forms ammonium hydroxide (NH₄OH).

Every new method of fertilization unfolds problems for investigation. The mere fact that a new type of fertilizer initially produces good economic returns is no guarantee of lasting efficiency. Since the continued use of a given fertilizer may deteriorate the chemical and physical properties of a soil and impair the crop yields, it is, therefore, of utmost importance to acquire a clear understanding of the reactions that take place and the resulting changes in soil properties.

In this paper are discussed certain fundamental problems of ammonia fertilization, especially those phases that require laboratory investigation. For the purpose of comparison with commonly used nitrogenous fertilizers, all experiments with ammonia (NH₃) were accompanied by corresponding experiments with ammonium sulfate [(NH₄)₂SO₄] or ammonium chloride (NH₄Cl). The various topics investigated may be conveniently grouped as follows: (1) the extent and chemical nature of ammonia fixation in soils; (2) the availability of ammonia in soils to plants and microörganisms; (3) the influence of ammonia on physical soil characteristics, especially permeability.

Fixation of Ammonium Compounds in Soils

Experimental Procedure.—To 50-gram portions of air-dry soil were added electrolyte solutions containing 2 to 500 milliequivalents of NH₄OH or (NH₄)₂SO₄. All systems were brought to a volume of 1 liter. The suspensions were kept at room temperature for 24 hours and were shaken occasionally. Samples of clear supernatant liquid were obtained by centrifuging or by means of Pasteur-Chamberland filters. According to special tests, no NH₃ was lost under the experimental conditions. The NH₃ was determined by distillation with MgO into standard acid, using methyl red as an indicator.