40 



FACTORS DETERMINING ENVIRONMENTAL 

 CONDITIONS. 



XXVI. E. j. Russell. "Hie PJiysico-Chemical Problems 



relating to the Soil.'* Trans. Faraday Society, 

 1922. Vol. XVII. pp. 219-22:1 



A g-eneral survey of the physico-chemical factors operating in 

 the soil and their influence on fertility. The soil is regarded as 

 a system formed of four components : (i.) mineral particles; being- 

 disintegrated and decomposed rock fragments which, through the 

 action of weather, water, ice and other factors, have in course of 

 time been reduced to dimensions varying from about 1 mm. in 

 diameter to molecular orders of magnitude. (ii.) Colloidal 

 material ; either very fine particles or a jelly coating the larger 

 particles and consisting of materials such as precipitated oxides of 

 iron and aluminium, silicia, etc., or both, (iii.) Intermingled in 

 most intimate fashion with this is the organic matter, residues of 

 past generations of plants and animals, which represents the 

 source of energy for the large population of soil organisms, 

 (iv.) The soil solution, being the soil w^ater and everything 

 dissolved therein. The whole mass is permeated with air. It is 

 shown that the agricultural and physical properties of the soil can 

 to a considerable extent be explained by such a system, but there 

 are facts which do not as yet readily fit it. 



A more detailed discussion of certain aspects of the subject is 

 given in the following three papers. 



XXVII. H. J. Page. "The Part Played by Organic Matter 



in the Soil System." Trans. Faraday Society, 

 1922. Vol. XVII. pp. 272-287. 



The influence of the humic material of the soil, on the physical 

 and physico-chemical properties of the soil is discussed. Owing 

 to the colloidal nature of this humic material, its chemical nature 

 and mode of formation are still little understood. The established 

 agricultural practice of using dung, green manures, etc., to 

 maintain the fertility of the soil, however, depends in a large 

 degree on the colloidal nature of the humic material derived from 

 such organic manures ; even without more knowledge of the 

 chemical nature of humus, its effect on tilth, moisture relationships, 

 supply of plant nutrients, and soil reaction can be explained, at 

 any rate on broad lines, in terms of its physical, i.e., colloidal, 

 properties. 



XXVIII. B. A. Keen. "The System Soil— Soil Moisture." 



Trans. Faraday Society, 1922. Vol. XVII. 

 pp. 228-243. 



A general discussion of the relations existing between the soil 

 and its moisture content, with especial reference to the physical 

 significance of the various divisions of soil moisture that have 

 been proposed from time to time. 



XXIX. E. M. Ckowthek. "Soil Acidity in its Physico- 



Chemical Aspects." Trans. Faradav Society, 

 1922. Vol. XVII. pp. 317-320. 



