722 EXPERIMENT STATION RECORD. [Vol.33 



It is thought that instructive conclusions may be drawn from the process 

 of base exchange in soils regarding soil-forming factors and also the physical 

 and chemical soil properties. 



The cause and nature of soil acidity with special regard to colloids and 

 adsorption, E. Truog (Jour. Phys. Chem., 20 {1916), No. 6, pp. Jt57-Jf84,' «?>«. in 

 Chcm. Abs., 10 {1916), No. 18, p. 2381).— This is a review of a large amount of 

 literature bearing on the subject and a general summary of the results of the 

 laboratory research work on the subject at the Wisconsin Experiment Station. 



It is maintained that the existence of selective adsorption of ions from the com- 

 mon alkali and alkaline earth salts is questionable. " The phenomenon observed in 

 acid soils and often designated as selective adsorption of ions is of an entirely 

 higher order in extent, and comparable in every way to chemical reactions be- 

 tween acids, bases, etc. ... It is shown that, when the conditions are properly 

 controlled, it can be demonstrated that the reactions due to soil acidity take 

 place according to chemical equivalence and exhibit all the properties of true 

 chemical reactions. 



" The possibilities for the formation of true acid substances in soils of the 

 humid region are manifold and it would be extremely difficult to explain why 

 such substances should not be formed. In most upland soils mineral acids, i. e., 

 kaolinite and other acid silicates, are the main cause of soil acidity. Soils high 

 in organic matter may contain considerable amounts of organic acids. These 

 acid substances may be either in the crystalloidal or colloidal condition and 

 their acid reaction is due to their chemical nature and not colloidal condition." 



Preliminary studies on heated soils, J. Johnson {Science, n. ser., ^3 {1916), 

 No. 1108, pp. IfSIi, .'f35). — The results of experiments conducted at the University 

 of Wisconsin are reported. It was attempted mainly to correlate the chemical 

 changes produced in heated soils with their effect upon seed germination 

 and plant growth. The conclusions drawn are considered to apply particu- 

 larly to soils heated above 100° C. Various seeds were used, especial use 

 being made of cabbage. 



"The results in general were similar for the different seeds, though they 

 varied much in their susceptibility to the injurious action. Lettuce and clover 

 seeds were very susceptible to the injurious action of highly heated soils, 

 whereas rye and buckwheat were very resistant. Plant growth is affected in 

 much the same manner, wheat, for example, recovering rapidly from the delete- 

 rious action of certain heated soils where tomatoes appeared to be permanently 

 injured. 



" Different soils give markedly different results upon heating to the same 

 temperatures. The action appears to be dependent particularly upon the con- 

 tent of organic matter in the heated soil. . . . 



" The temperature to which the soil is heated is seemingly the most impor- 

 tant factor in determining the extent of the injurious or beneficial action. 

 Approximately 250° was found to be the most critical temperature in all the 

 soils used. At this temperature seed germination was most strikingly retarded. 

 Early plant growth was usually checked for the longest period of time on 

 soils heated to 2.50°, although late plant growth, in the case of some crops at 

 least, was most vigorous on these soils. Heating to temperatures of 300', or 

 above, in all the soils used again reduced the injurious action to seed germina- 

 tion and early plant growth, as well as the beneficial action to late plant 

 growth. Heating soils to 2.50° produced greater amounts of material extract- 

 able with water than heating to higher or lower temperatures. The ammonia 

 content of the soil increased proportionally to the temperature of heating up 



