This study deals with the basic agronomic and economic relationships of fertilizer use. It is the second in a series of methodological studies designed to predict production surfaces, isoquants, isoclines, marginal products and marginal replacement rates between nutrients when two or more nutrients are used in promoting increased crop yields. These quantities, which are fundamental in obtaining a basic science knowledge of fertilizer-crop relationships, are then used to predict optimum levels of fertilization and optimum ratios of nutrients with profit maximization as the criterion of selection. While the major objectives of the study are of a methodological nature, illustrations are included to show how the basic relationships and principles can be adapted to simple forms for farmer and educational uses.

The logical foundations for research of the type reported in this bulletin are reported elsewhere.² The production functions and economic optima predicted in this study are for corn on three types of soils with two and three nutrients variable in quantity.