418 NATURE AND PROPERTIES OF SOILS 



230. Relation of soil conditions to nitrification.— Al- 

 though a very great number of factors influence the process 

 of nitrification, the principal controls may be listed as fol- 

 lows: (1) presence of nitrifiable substance, (2) aeration, (3) 

 temperature, (4) moisture, (5) soil reaction, and (6) the 

 presence of soluble salts. 



A peculiarity in the artificial cultivation of nitrifying bac- 

 teria is that they cannot be grown in artificial media con- 

 taining organic matter. In the soil, however, organic matter, 

 "When well decayed, stimulates nitrification,^ provided aera- 

 tion and other conditions are favorable (see par. 313). The 

 application of twenty tons of farm manure to the acre to sod 

 on a clay loam soil for three consecutive years, at Cornell 

 University,^ resulted in a larger accumulation and probably 

 a larger production of nitrates on the manured soils than 

 on a contiguous plat of similar soil left unmanured. This 

 was especially true during the third year of the application, 

 when the land was in sod, and also during the fourth year, 

 when no manure was applied to either plat and when both 

 plats were planted to maize, as may be seen from Table XC 

 (page 419). 



These data indicate not only a marked influence of organic 

 matter on nitrification but also an effect from aeration. Even 

 allowing for a direct and differential influence on nitrifica- 

 i>ion by the two crops, it is evident that tillage is a factor. 

 Further experimental data from Cornell University may be 

 quoted. Columns of soil eight inches in diameter and eight 

 inches in depth were removed from a field of clay loam on 

 the Cornell University farm and carried to the greenhouse 

 without disturbing the original structure of the soil. At 

 the same time, vessels of similar size were filled with soil dug 

 from a spot near by. These may be termed unaerated and 



^The turning under of a green-manuring crop generally depresses 

 nitrification at first. Once the decay process is well under way, nitrifica- 

 tion activities seem to be stimulated. 



^ Unpublished data. Cornell Agr. Exp. Sta., Ithaca, N. Y. 



