THE GERM LIFE OF THE SOIL 



139 



inoculation. The conditions favorable for legumes are the 

 same as for most upland crops, namely good drainage and 

 good tilth, while for red clover, peas or alfalfa the soil should 

 have an abundant supply of lime. 



Not only is the yield of an alfalfa crop greatly increased 

 by the presence of the nitrogen-fixing organisms and also 



Nitrogen of air 



$b animal 



r#EE F/XAJjO/i 

 Free m'fi 



troden Comdex. compou/M, 



DiWTRIFICATIOn '.-• ;. 



WTRIFICATICM 



0/4 



ri _ 



decay..- y 



- inTERMEDlATC PfZODUCTi 

 Carbon dioxide, etc 



4M/10MA 



Fig. 25. — The cycle through which nitrogen passes in its movements 

 among soil, plant, animal and atmosphere. Solid lines in the diagram indi- 

 cate the usual transformations of nitrogen. Dotted lines indicate the occa- 

 sional transformations. 



of lime, but the percentage of nitrogen that the crop contains 

 is thereby increased. 



178. Nitrogen fixation by free living germs. — In addi- 

 tion to the nitrogen-fixing bacteria described above, there 

 exist in many soils germs that are able to take nitrogen from 

 the atmosphere and convert it into nitrogenous organic mat- 

 ter without the aid of a host plant. How extensively these 

 organisms operate is difficult to say. In poor land they are 

 often effective in recouping the supply of soil nitrogen, but 

 it is doubtful to what extent they function in rich soil. At 

 the Rothamsted Experiment Station one of the fields had 

 been allowed to lie unused for many years because it was too 



