Experimental work conducted by the Soils Section of the Iowa Agricultural Experiment Station and the cooperative field experiments have Indicated that certain fertilizers are needed on many Iowa soils and that they can be applied with profit. There are many soils, how· ever, which cannot be reached by such tests and there are many problems connected with the use of fertilizers on Individual farms which can only be solved by the farmers themselves. Simple tests on the farm arc of value In determining the need of and the profit which may be secured from the use of certain fertilizers. This circular attempts to present briefly facts regarding fertilizers and their use In Iowa. We hope farmers will become interested in testing the value of these materials. A knowledge of the facts, we believe, will aid In preventing a waste of money and energy thru the use of inferior and unprofitable fertilizers.