The intensity of removal of added cations from soil colloids by electrodialysis

Information is presented which supports the suggestion that there is a close relationship between the oxidation-reduction potentials of nutrient materials and the intensity of their removal from soil complexes by electrodialysis. Samples of soil were electrodialyzed for 24 hours and definite amounts of soil were treated with a single salt solution. A composite sample made from the soil samples treated with potassium and calcium chlorides was electrodialyzed for 32 hours. Samples of the diffusate were collected at 2-hour intervals for the first 16 hours and at 8-hour intervals for the second 16 hours. Soil samples containing a single added cation were electrodialyzed in a similar manner. The data presented illustrate very clearly the differential in intensity of removal of the various metals from soils by electrodialysis. There is a correlation between the intensity of removal of certain cations from soils and the strength of ions. The strongest ions are removed most rapidly from the soil. A large proportion of the strong cations was found in the first two fractions of the diffusate. Oxidation-reduction potential values and ionization-potential values are useful in predicting the intensity of removal of cations from soils by electrodialysis. The adsorption and removal of an electrolyte from a soil appears as in additive property of its ions. It appears that the quantitative adsorption and removal of any individual added cation is probably influenced by the solubility of the compound or compounds it may form in the soil complex. Added sodium and calcium which apparently form relatively soluble complexes in the soil may be removed more completely than added potassium which apparently forms certain relatively insoluble compounds in the soil. The solubility values of various electrolytes may be of great value in an interpretation of some of the striking growth responses of crops observed from inadequate or excessive amounts of the so-called minor plant nutrients. In areas using heavy applications of commercial fertilizer the insufficient quantities of the minor plant nutrients in the soil are often the limiting factors in determining crop yields.