Soil Fertility and Its Preservation 47 



ceeding crop to be abun- 

 dant, for this crop will 

 use the nitrogen that 

 has been gathered by 

 the green manuring 

 crop. (Exp. 4.) 



It has been found that 

 inoculating a field with 

 the right kind of bac- 

 teria is sometimes of 

 considerable benefit to 

 a leguminous crop. This 

 is done in two ways. 

 Either (i) a few hundred 

 pounds of the topsoil 

 from a field where the 

 same crop has been 



growing may be added to each acre of the new field ; 

 or (2) the seeds to be planted may be soaked in water 

 to which a " pure culture " of the bacteria has been 

 added (Fig. 31). When the seeds germinate, the 

 bacteria will be near at hand to work upon the roots. 

 Cultures of nitrogen-fixing bacteria for various legumi- 

 nous crops are on the market, and they may also be 

 secured from the Bureau of Plant Industry at Wash- 

 ington. It is not always necessary to inoculate a new 

 field, for the needed bacteria may already be there living 

 on wild clover or other legumes. 



There are other kinds of bacteria that make nitrogen 

 available for crop plants. They do not live upon the 

 roots of legumes but feed upon dead vegetable and ani- 



How 

 friendly 

 bacteria 

 may be 

 added to 

 the soil 



W. T. Sktlllng 

 FIG. 30. Bean roots, showing nodules. 



Encourag- 

 ing other 

 useful 

 bacteria 



