330 Microorganisms and Soil Fertility 



Table 74. Ixfluence of Fungi on Soil Aggregation (from Swaby) 



Totals 50 31 19 



Soil Inoculation 



It often becomes necessary to introduce into the soil bacteria and 

 certain other microorganisms that may be lacking there. Among 

 these, root-nodule bacteria occupy a pre-eminent place, as brought 

 out previously. At first, soil in which the legume was grown suc- 

 cessfully was used for inoculation. Soon after, however, artificial 

 cultures in liquid and solid media were substituted for the soil. In 

 recent years, peat material has been utilized as a carrier for legume 

 bacteria. 



Although soils in which legumes have once grown contain for 

 some time the organisms responsible for formation of nodules on 

 the corresponding plants, it was found that these bacteria may de- 

 teriorate in the soil, either by loss of vitality or through the effect 

 of antagonistic microorganisms. It may, therefore, become advisable 

 to inoculate a soil frequently for a certain legume. The existence of 

 various strains of bacteria, which vary greatly in activity, the forma- 

 tion of bacteriophages active against the specific bacteria, and the 

 potential effect of antibiotics produced by other microorganisms 

 lead more and more to recognition of the importance of repeated 

 inoculation of soils with vigorous cultures of organisms. 



On a much smaller scale, but of potential importance, are the 

 mycorrhiza fungi. These are capable of producing associations with 

 various higher plants, notably certain evergreens, resulting in in- 

 creased plant growth. It has been found advisable to inoculate 

 nursery beds with a small amount of soil from an old bed in which 

 the corresponding trees have been grown successfully. So far, no 

 pure cultures of fungi have been utilized for this purpose. In cer- 



