ORGANIC CONSTITUENTS OF THE SOIL SOLUTION IO3 



methods are no less important in field practice than are fertilizers 

 in promoting this important activity of plants. There is little 

 reason to doubt that oxidizing agencies other than plant roots 

 (bacterial for instance) are more or less active in every arable 

 soil, and numerous investigations, among which Russell's 

 researches 1 are conspicuous, leave little doubt that oxidatoin 

 processes are promoted by good tilth. It is apparent, therefore, 

 that by the activities of the plant itself as well as other agencies, 

 the general tendency in soils is the destruction of or rendering 

 innocuous harmful plant effluvia or other organic substances, and 

 to this end are effective each of the three methods of soil control 

 generally practiced, namely, tillage, crop rotation and fertilizers. 



Among the organic components of the soil none have greater 

 importance and interest than those containing nitrogen or as 

 they are frequently called the nitrogen carriers. Conspicuous 

 among these are the nitrates. While it is now generally conceded 

 that ammonia and other nitrogen compounds can be taken up 

 by higher plants and elaborated by them under special conditions, 

 it nevertheless remains true that plants draw their needed supplies 

 of nitrogen from the soil solution, mainly in the form of nitrates. 

 The problems presented by these nitrogen carriers are mainly 

 bacterial 2 and physiological, but certain features are of direct 

 importance to the soil chemist and to a study of the soil solution. 

 It is now known generally that there are many kinds of nitrifying 

 and denitrifying bacteria in soils, and that probably every arable 

 soil contains several species, or varieties at least of both kinds. 

 With good tilth and consequent aerobic conditions, nitrifying 

 processes prevail, and with poor tilth or in subsoils, anaerobic 



1 Oxidation in soils, and its connection with fertility, by Edward J. 

 Russell: Jour. Agric. Sci., 1, 261-279 (1905) ; Pt. II. The influence of 

 partial sterilization, by Francis V. Darbishire and Edward J. Russell, 2, 

 305-326 (1907). 



* The fixation of atmospheric nitrogen by bacteria, by J. G. Lipman, 

 Bull. 81, Bureau of Chemistry, U. S. Dept. of Agriculture, 1904, pp. 146- 

 160; A review of investigations in soil bacteriology, by Edward B. Voor- 

 hees and Jacob G. Lipman, Bull. 194, Office of Experiment Stations, U. S. 

 Dept. of Agriculture, 1907. 



