30 BULLETIN "E." 



Mean observed amount of nitrates in soils to which was added 



If, however, the soils are classed, as has before been done, 

 into the poorer and stronger groups and a comparison of the 

 nitrification made, the results will stand as given in the next 

 table. 



Relation of nitrification to fertilization. 



From this comparison it appears that the addition of ma- 

 nure to the four poorer soils has augmented the development of 

 nitrates and in amounts increasing with the manure added. 

 The guano, however, appears to have had a, depressing effect. 

 In the case of the four stronger soils, the two larger amounts 

 of manure added appear to have retarded the accumulation of 

 nitrates in the soil; while the guano may have increased the 

 amount The two groups of soils, therefore, hold opposite re- 

 lations as regards the influence the manure has had upon their 

 nitrate content. Such relations as these have been many times 

 noted by different observers and it is unfortunate that it has 

 not yet been clearly demonstrated to what causes such rela- 

 tions should be ascribed. 



It is worthy of special remark that notwithstanding the 

 greater effect of the manure in increasing the nitric acid con- 

 tent measured in the four poorer soils, there is, nevertheless, a 

 greater difference as regards nitrates between these two groups 



