Sept. ii, 1916 



Bacteriological Studies of a Soil 



973 



Table XI. — Quantity (in milligrams per 100 grams of soil) of nitrate in soil when 

 sampled from fertility plots at Columbia, Mo., in IQI3 and 1914 a 



a Soil was dried at no" C. for two hours. 



SUMMARY 



(1) The agricultural methods practiced upon the plots under study 

 have brought about marked differences in the number of organisms con- 

 tained in the soil, at least those capable of developing under our experi- 

 mental conditions. The soil under continuous corn and wheat contains, 

 in the absence of any additions of fertilizers or manure, relatively low 

 numbers of bacteria. In the presence of manure, continuous corn and 

 wheat soil contain relatively high numbers, manure having a much more 

 marked effect upon numbers here than under the other crops studied. 



(2) The agricultural practices under study have, so far as we can 

 detect without experimental methods, produced no appreciable effect 

 upon the ability of the soil and its organic life to liberate ammonia from 

 cottonseed meal. 



(3) The ability of the soil complex to oxidize ammonia nitrogen to 

 nitrate nitrogen has been materially altered by the methods under study. 

 This we believe to be due in part to physical and chemical changes in the 

 soil and in part to biological changes. Continuous corn and wheat with 

 no additions of manure or chemicals have brought about a relative low 

 oxidizing power in the soil complex. The addition of manure materially 

 raises the oxidizing power, especially under continuous corn and wheat. 

 The addition of commercial fertilizer brings about a condition similar to 

 that of manure, though perhaps less marked. 



