Effects of Soluble Salts on Insoluble Phosphates.’

This study has been taken up from two viewpoints. First, a study of field and pot experiments, with a view of determining, if possible, the indirect action of various salts when used as fertilizers; to ascertain if the increase in yield obtained from the use of a fertilizer is not due in part to the solvent action which it exerts on the comparatively insoluble phosphorus in the soil. Second, to study in the laboratory, the solvent action of the more common salts on phosphates, using distilled water as a standard. That some fertilizers have an indirect effect has long been an acknowledged fact. It is no longer believed, that the increase in yield obtained from the use of one ton of barnyard manure, is alone due to the addition of the two or three pounds of phosphorus and the ten or twelve pounds each of nitrogen and potassium which it contains; but no small part of the increase is due to the liberation of more plant food. This (I) is brought about by the decaying of organic matter with the formation of various acids which in turn act as solvents on insoluble plant food already in the soil. The benefits obtained from the use of gypsum and lime are due not only to the neutralizing of acid and supplying of calcium, but it is acknowledged that they act indirectly by liberating potassium. From certain results obtained in various experiments, which will be considered later, it seems as if this may be due in part, to the liberation of phosphorus from its less soluble forms.