412 



MICROBIOLOGY OF SOIL 



possible the successful growing of alfalfa in almost any soil, while the 

 leguminous vegetation of limestone soils is proverbially vigorous. 

 The favorable influence of lime is due to the direct action on the plants 

 as well as on the bacteria in the soil. Similarly, the tubercle bacteria 

 are favorably affected in their survival and multiplication by an 

 abundant supply of organic matter. On the other hand, acid soils or 

 those deficient in humus and inadequately aerated are but ill suited 

 to the activities of Ps. radicicola. 



FIG. 136. Roots of Plant A without nodules (Fig. 135). 



SOIL INOCULATION* 



By soil inoculation is now understood the adoption of some 

 artificial method for supplying suitable quantities of nitrogen-fixing 

 organisms to soils deficient in these types. The first attempts at soil 

 inoculation were made in 1886 by Hellriegel and Wilfarth during the 



* Prepared by S. F. Edwards. 



