JACOB G. LIPMAN 349 



as insecticides and fungicides rather than for partial soil sterilization. Elementary 

 sulphur is employed for the same purpose, for it is rapidly oxidized in the soil to 

 sulphuric acid. By increasing the hydrogen-ion concentration of the soil it renders the 

 latter a less fit medium for the survival and development of certain micro-organisms. 



The experience with volatile antiseptics and germicides has given us a better in- 

 sight into the true character of the soil microflora and fauna. Numerous experimental 

 studies have shown that partial soil sterilization disturbs the microbiological balance, 

 that the initial reduction in numbers is followed by an abnormal increase in the num- 

 bers of bacteria, and that partially sterilized soils become very productive for a time 

 at least. More recently the attention of microbiologists has been drawn to the partial 

 soil sterilization that occurs in some arid and semi-arid regions because of the more 

 or less thorough drying of the surface material and its exposure to the intense desert 

 heat. Such land, during the rainy reason, or when supplied with irrigation water, 

 behaves not unlike soil partially sterilized by artificial heat or volatile antiseptics. 

 There is reason to beheve that the study of partial soil sterilization will point the way 

 toward better control of soil-fertility factors and the more effective use of micro- 

 organisms for the mobilization of plant food. 



Soil inoculation is no longer an empirical practice. It is claimed that the scatter- 

 ing of rich garden soil on newly reclaimed peat bogs was practiced in Finland more 

 than a hundred years ago. The preparation of composts and the use of composted 

 earth became a fine art in the Orient long before the beginning of the present era. 

 Manure and other waste materials are still widely used in Europe for the preparation 

 of composts, although high labor costs and the abundance and cheapness of chemical 

 fertilizers have discouraged compost-making in Western Europe and North America. 

 The improvement in the methods of producing activated sludge promises to make 

 this material a means of conserving much of the plant food that is now sewered into 

 the sea. The use of animal manures has already been mentioned. Together with com- 

 posts and activated sludge, it may be utilized for mass infection, as well as for the 

 addition to the soil of nitrogen and of other plant-food constituents. 



In a more particular way soil inoculation is practiced with Thiobacillus thiooxidans 

 and Bact. radicicola. In the case of the former, ground brimstone employed for the 

 control of potato and sweet-potato diseases, the correcting of the sulphur deficiencies 

 of certain soils, or the reclamation of black alkali soils, is inoculated with pure or crude 

 culture of the organisms. It has been observed in many instances that sulphur thus 

 inoculated is more rapidly oxidized when it is applied to the soil. 



Inoculation with Bact. radicicola is widely known and practiced. It was noted 

 above that rich garden soil was used in Finland at least as early as the eighteenth 

 century for the improvement of newly drained marshes. This empirical method was 

 observed to favor the establishment of clover. After the announcement by Hellriegel 

 and Wilfarth in 1886 that legumes in association with bacteria were able to fix at- 

 mospheric nitrogen, Tacke at Bremen introduced the use of earth from clover and 

 other legume fields. Inoculation by means of legume earth is still being practiced in 

 Europe and North America. In the United States soil from old alfalfa fields is still 

 occasionally employed for inoculating new alfalfa fields. On the whole, however, 

 pure cultures of Bact. radicicola are used in preference for inoculating the seeds of 



