NON-SYMBIOTIC NITROGEN FIXATION 145 



These come from the plant and animal residues brought to the 

 soil and differ in value with various substances, as may be seen 

 from the following: 



Material 



Nitrogen Fixed in lOO cc, of 

 Solution after J Weeks (mgrn.) 



Fresh Straw 



Fresh Stable Manure 



Fresh Peat 



Green Manure 



Beijernick*s Mannite Solution 



lO.O 



9.8 



9-3 

 8.0 



S.6 



After humiiication these substances are even more readily as- 

 similated and the nitrogen fixation greater than when the un- 

 humified substance is used. 



Other workers have found that stable manure, even up to 3 

 per cent, greatly stimulated bacterial activities. It is certain that 

 humus can act as a source of energy and usually stimulates bac- 

 teria, but the extent is governed largely by its composition and 

 by the quantity of available combined nitrogen which is being 

 supplied with it to the organism. In addition to this, corn roots, 

 corn stalks, oak leaves, lupine, alfalfa, maple leaves, and pine 

 needles may all serve as a useful source of energy to the nitro- 

 gen-fixing organisms. Apparently the tissues from the non- 

 legume giYt a greater gain than do those from the legumes. 



The influence of stable manure upon the nitrogen-fixing pow- 

 ers of the soil under field conditions is seen from the following 

 results obtained by the senior author. The nitrogen fixed in 

 the unmanured soil is taken as 100 per cent. 



Treatment 



Nitrogen Fixed {Per cent) 



No manure 



100 



5 Tons of Manure per Acre 



103 



ID Tons of Manure per Acre 



no 



1 5 Tons of Manure per Acre 



105 



20 Tons of Manure per Acre 



103 



25 Tons of Manure per Acre 



101 



