Exchangeable sodium and the physical properties of soils

Abstract

In assessing the suitability of a water for irrigation purposes it has been customary to accept a set of limiting values for the concentrations of salt, free alkali, or total solids. These limits have been fixed somewhat arbitrarily from general experience, but this method is unreliable and does not enable accurate conclusions to be drawn as to possible deleterious effects of a given water on the soil and therefore on crops. The writer has used a different criterion for this purpose, and, as will be shown in the paper, it enables the true action, of the water on the soil to be predicted with some certainty. This criterion, which has been termed the 'Figure of Merit' of the water, is simply the ratio of the divalent ions calcium and magnesium to be monovalent ions sodium and potassium present in the water, all expressed as chemical equivalents.