Electrodialysis of Soils: III. Effect of Different Fertilizer Treatments of Soils on the Bases and Acids Extracted by Electrodialysis 1

Ever since the earliest investigations along soil fertility lines, attempts have ,been made to devise methods which would show the amounts of the necessary plant-food constituents present in the soil in an available form. At first it was thought that a determination by chemical analysi s of the presence in the soil of the total amounts of the different elements used ,by plants would indicate the amounts available. But it was soon found that, although an element needed for plant growth might be present in the soil in a considerable amount, this would not necessarily mean that there would be an adequate amount present in such a form as to be available. In recent years many experiments have attempted to give an insight into the state in which the various elements must occur to be available to plants. It has been shown that plant food must be it~ solution to be able to pass through the membranes of the root hairs into the cell sap of the plant. Hence it has seemed evident that the plant food must be in soluti’.on in the soil moisture in order to be of use.to plants. This has led to the development of methods for the extraction of availaNe plant foods by the use of water. Among these, methods the more important ones involve leaching the soil with water, or shaking the soil with certain amounts of water for different lengths of time. It has been shown, however, that’these methods fall short of the objective sought, for it is known that plants take up much larger amounts of certain elements than arc found to be present when these water extracts are analyzed. The chief