THE INFLUENCE OF SOIL CONDITIONS ON THE 

 DECOMPOSITION OF ORGANIC MATTER IN 

 THE SOIL. 



By E. J. RUSSELL, D.Sc. and A. APPLEYARD, M.Sc. 



(Rothanisted Experimental Station.) 



The biochemical decomposition of plant residues and other organic 

 matter in the soil is of fundamental importance for soil fertiHty. It 

 causes the breaking down of coarse plant fragments which otherwise 

 might open up the soil too much : it leads to the production of colloidal 

 complexes known as humus which exert many beneficial effects both 

 chemical and physical, and it brings about the formation of nitrates, 

 the most important of the nitrogenous plant nutrients. 



The decomposition has been studied extensively in the laboratory 

 and its general course has been fairly satisfactorily determined ; but 

 there has not been much work in the field. The difficulties of field 

 work are of course very considerable, but it has the enormous advan- 

 tage, which in the nature of things laboratory work cannot possess, 

 that it is affected by all the factors concerned, and can therefore be 

 made to reveal them. The detailed study of the way in which each 

 factor operates can then be made in the laboratory. 



In large part the decomposition is brought about by bacteria and 

 other micro-organisms. No definite connection, however, has been 

 traced in the field between the activity of the micro-organisms and the 

 extent of the change. It is difficult to measure bacterial activity with- 

 out using some decomposition and therefore begging the whole question 

 as to its relationship with decompositions : the only method that does 

 not involve this is to count the bacteria by some dilution or plating out 

 method. This has been done by several investigators, but no particular 

 relationship has been observed. In most cases a comparison has been 

 made between different plots of known productiveness with the view 



