MANURING AND WORN-OUT SOILS 335 



way to introduce the needful bacteria is to buy 

 one of the several artificial cultures. Of these, 

 "nitro-culture" is probably most widely known. 

 These preparations contain a large quantity of the 

 bacteria somewhat as a yeast-cake contains the 

 bacteria that make bread rise. The "soil yeast- 

 cake" is dissolved in warm water and this water 

 sprinkled on a quantity of soil, which is then dis- 

 tributed on the new land. Very uncertain results 

 have attended the use of nitro-culture and similar 

 preparations; in some cases the soil has been in- 

 oculated ;with bacteria very successfully; in other 

 cases no beneficial results have followed. It is 

 evident that the method of preparing these cul- 

 tures has not yet been perfected. Undoubtedly the 

 use of artificial cultures of this and other beneficial 

 bacteria will some time become common and suc- 

 cessful, but at present the safest way is to get old 

 soil if it can be had. 



Some of those who are exploiting these preparations 

 have not made it clear, as they should, that in- 

 oculating the soil with this material assists none 

 but leguminous crops to secure nitrogen; and, 

 furthermore, that it may help to enrich the soil in 

 no plant food except nitrogen. The "yeast-cake'* 

 idea appeals strongly to the popular imagination 

 and the most absurd claims are sometimes made for 

 the artificial cultures. Soil inoculation is but 

 one of many means of maintaining fertility, and 

 usually it is a very incidental means. 



Each Crop has Different Bacteria. Not one kind 

 of bacteria performs this service, but many a differ- 

 ent kind on each leguminous crop. According to 

 present knowledge, the bacteria mat aid clover to 

 feed on nitrogen from the air, do not aid alfalfa, 

 cowpeas or any other crop. This means that one 



