The Efficiency of Certain Ammoniated Superphosphates and Other Phosphate Fertilizers 1

The .efficiency of different phosphate fertilizers has been much discussed ever since these fertilizers were first advocated for use. During the past 30 years, many investigators have given considerable attention to the economics of the use of different phosphate fertilizers, especially rock phosphate and superphosphate. The question of the relative value of these two phosphates has not been settled definitely, mainly because the efficiency of a fertilizer is affected by many physical, chemical, and biological soil factors. The basis of most laboratory tests for the availability of the plant food constituents of fertilizers is the assumption that the materials dissolving in some particular solvent are available for plant use. Crop response to the fertilizer, however, has not always been correlated with the solubility of the constituents and various solvents have been employed in the attempt to obtain a definite correlation. Since the earliest development of soil chemistry, it has been the hope of agricultural chemists to develop a simple, rapid test which would reveal the efficiency of different fertilizing materials without the necessity of time-consuming field experiments. As yet, however, there is no one method which will show accurately the efficiency of fertilizers when applied to different soil types. The recent achievement of producing anhydrous ammonia cheaply has made it economically possible to place on the market a fertilizer known as ammoniated superphosphate. Before this product came into use as a fertilizer, the phosphate soluble in neutral ammonium