Hygroscopicity of Fertilizer Salts

Abstract

A previous paper (1) a study was made of the hygroscopicities of various fertilizer materials and of mixtures of these having common ions. The nitrogen fixation products-calcium nitrate and ammonium nitrate, as well as urea-were found among the most hygroscopic of fertilizer materials. The fertilizer salts with two elements available for plant food-potassium nitrate, monopotassium phosphate, and monoammonium phosphate-proved to be the least hygroscopic of soluble materials. The hygroscopicity of a mixture was found, in general, to be greater than that of its more hygroscopic ingredient.The present paper reports the results of a similar study of mixtures of two fertilizer salts not having a common ion. Such salts are capable, by double decomposition, of giving a second salt pair, and systems involving such salts and water are known as reciprocal salt pairs.

Fertilizer Manual

“…A rather complex laboratory apparatus was used by USDA investigators to measure the water vapor pressure above saturated solutions of pure fertilizer salts and salt pairs (51,53).…”

“…In preparing humidity-control solutions, a suitable salt or salt pair is first selected from published vapor pressure data (51,52,53). Procedure is generally the same as with the more sophisticated cabinet, except that time must be allowed for air-solution equilibrium to be reached, and door openings must be minimized to retain humidity.…”

Hygroscopicity of Fertilizer Mixtures

“…Comparative experiments were carried out with superphosphate and double superphosphate. (12) Glancy, Wright, and Oon, Ind. Eng.…”

Preparation of Physiologically Neutral Fertilizer Mixtures - Reactions of Monoammonium Phosphate with Limestone and with Dolomite

“…When superphosphate is mixed with ammonium sulfate, as is now common practice in the preparation of mixed fertilizers, reaction may take place between the ammonium sulfate and the monocalcium phosphate in the superphosphate: Ca(H2PO")2 + ( 4)28 4 = CaS04 + 2NH4H2P04 Merz and his co-workers (7) have shown that calcium sulfate and monoammonium phosphate are the stable pair of these reciprocal salt pairs. A mixture of monocalcium phosphate and ammonium sulfate containing an excess of the former will therefore react in the presence of moisture until the ammonium sulfate no longer exists in the solid phase.…”