20 



Historical 



These methods were variously modified, according to the nature 

 of the substances added to the soil and the processes studied. Ni- 

 trates were utilized for stimulating the growth of nitrate-reducing 

 organisms, which produced nitrite, ammonia, or gaseous nitrogen. 

 Cellulose was used to bring about the development of cellulose- 



FiG. 13. F. Lohnis wrote the first comprehensi\e book on soil bacteriology; he 

 also studied the methods for the evaluation of the role of bacteria in soil fertility. 



decomposing bacteria. The evolution of ammonia and the forma- 

 tion of nitrates also found application in determining the liberation 

 of nitrogen from fertilizer materials, especially of organic origin. 

 Hopes were aroused that the results thus obtained would find appli- 

 cation in the measurement of soil fertility. It was believed that 

 such methods could be utilized for routine examination of soils to 

 foretell their potential productive capacity. 



Unfortimately, the results obtained by those methods did not 

 justify the expectations. After thousands of tests had been made 



