Bulletin No. 170 - A Study of Methods of Determining Soil Alkali

There is a great lack of uniformity in the methods of testing soils for alkali salts and in the forms of expressing the results in a way that will show the relative toxicity of the salts. This has been pointed out by numerous investigators and has been shown to complicate the determinations so much that the results of different investigators are hardly comparable. It is of further disadvantage in that the toxic limits of an alkali as worked out by one system of analysis are often difficultly applicable to a soil that has been tested by another system. However, it is not easy to establish an arbitrary standard method because each method has advantages and disadvantages and each investigator probably uses the method that is most adapted to his own problem. It is doubtful if any methods now in use really give an accurate conception of the actual alkali composition of the soil solution. This bulletin reports some comparisons of different methods of testing alkali soils both as to results and relative variability, a study of some of the irregularities in the water-extraction method of testing for sodium carbonate, and a study of crop germination as an indication of alkalinity. From these it endeavors to establish not the accuracy of any method of testing a soil for alkali, but if possible something of the toxic limits of alkali soils as shown by various tests with some idea as to the relative variations in the results