73 



loam types. The averages from nitrification tests in these soils are consid- 

 erably in advance of the others. The conspicuous increase in the clay loam, 

 from a relatively small number of soils it is true, is one of the most striking 

 results recorded. Apparently in soils of this type, carrying a fair amount 

 of organic matter, a condition for maximum nitrification is obtained. 



The gradation in the nitrifying power of these virgin soils is extremely 

 interesting the scant formation of nitrates in sandy soils, the pronounced 

 increase in loams and clay loams, and the depression of nitrification in 

 heavy clay soils are indeed noteworthy. 



In considering the influence of soil types on nitrification it will be well 

 to inquire first how far cultivation will go in obliterating the differences 

 which previously have been discussed. By singling out from Table I a 

 number of cultivated soils which show high nitrifying powers, one from 

 each of the five general classes, some idea may be obtained of the possibilities 

 which each soil type presents. Such figures are presented in Table No. IV. 



TABLE IV. Giving the Nitrifying Efficiency of a Number of Cultivated 

 Soils of Various Types. 



The figures in Table IV are maximum results from cultivated 1 soils of 

 the respective types. The sandy soils are yet notoriously low, the loams and 

 clay loam are high, the clay soil has responded to cultivation and presents 

 a high nitrifying power. Although the maximum figure for sandy soils is 

 low in the present investigation, such has not always been our -experience 

 with these soils. A previous report of a Norfolk soil which for five years 

 received crimson clover turned under as green manure and yearly applica- 

 tion of lime, showed a formation of 27.7 mgs. nitrate nitrogen per 100 grams 

 of soil. It is possible, therefore, to develop soils of that type to a high de- 

 gree of nitrifying power. 



Of course the above results are from isolated cases and are not worthy 

 of general conclusions. They are given merely to illustrate the possibilities 

 which most soils probably possess from the standpoint of nitrification as 

 promoted by the proper type of cultivation. 



The relationship which nitrification and nitrogen fixation bear to one 

 another was observed with interest throughout the present investigation. 



