It has "been observed for many years that ammonium sulfate has in time produced ah infertile condition in a soil to which it is applied year after year. This thesis demonstrates (a) that this salt forms soluble sulfates by an exchange with the bases existing in the soil and (b) that these are freely removed in the drainage water. In the prese nce of much calcium carbonate, the formation of calcium sulfate occurs more prominently than any other salt. In its absence , the sulfates of iron, aluminium and manganese are formed, resulting in a marked change in the absorptive properties of the soil. These salts upon hydrolysis give a positively acid reaction and cultures in them of different kinds of seedlings showed them to be toxic in relatively low concentration.