CHAPTER XIV 



THE RECENT WORK ON THE BIOCHEMICAL PROCESSES 

 OF THE SOIL 



I. Soil Protozoa. III. Biochemical Reactions. 



II. Sick Soils. References. 



REFERENCE has already been made to the fact that nitrification, 

 the process by which the nitrate indispensable to plant growth is 

 made in the soil, is the work of micro-organisms. The investiga- 

 tions of Schloesing and Miintz, of Warington and of 

 Winogradsky, led to a prodigious number of others, and soil 

 bacteriology has now grown into a very large subject. It is 

 now known that the soil is teeming with life, and that a 

 single saltspoonful of it contains millions of organisms, 

 living, ^working, and multiplying, and among other activities 

 bringing about various changes absolutely indispensable to 

 plant growth. 



The development of the subject has taken place in three 

 directions. Efforts have been made to discover and then to 

 describe the organisms concerned in the processes. Chemists 

 have tried to find out the steps by which the decomposition 

 proceeds. At Rothamsted investigation has been directed to 

 the discovery of the conditions under which the organisms 

 live and work, with the view of ultimately obtaining some 

 degree of control over them. 



So impressed were the earlier investigators with the great 

 part played by bacteria, that these came to be tacitly regarded 

 as the only organisms concerned. But a number of difficulties 

 and anomalies arose when the work was carried from the 

 laboratory into the field, and efforts were made to connect the 



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