Properties of Colloids from Dry Land Soils

Numerous investigations of the chemical and physical properties of soil, both in the United States and elsewhere, have shown very definitely that the colloidal portion of the soil is of primary importance. it has been shown that a given soil series is characterized by a colloid of striking uniformity of composition (8), particularly with reference to the major components and their interrelationships. In like manner, the great soil groups have been shown to be characterized by colloids of markedly divergent types. (1) It has become increasingly apparent since the work of Cushman (6), and Gushman & Hubbard (7) that the hydrolysis of minerals is the dominant chemical process in the production of the colloid, although its final character is Influenced by various chemical and physical processes. In various publications the importance of different influences have been stressed. Robinson and Holmes (11), and Reifenburg (10) have emphasized the importance of rainfall, while Crother (5) and Jenny (9) have stressed the influence of temperature. Brown, Rice and Byers (2) examined a series of soils from Nebraska which, under a fairly wide variation in rainfall, showed small differences In colloid character, although there are wide differences in distribution within the profile. In a paper, now in press, Brown and Byers (J) have examined carefully a series of soils whose distinctive environmental condition is a difference in temperature. In order to obtain the temperature range desired soils from diverse parent material had to be selected. However, all fall in the division of Pedocal soils.. Complete data concerning the soils and their colloids, as well as methods of treatment and analysis, will be presented in the above-mentioned publication (J). Here we will be principally concerned with the colloids, and a portion of the data concerning them.