440 NATURE AND PROPERTIES OF SOILS 



Within recent years a number of cultures for soil inocula- 

 tion have been offered to the public. The first of these util- 

 ized absorbent cotton to transmit the bacteria in a dry state 

 from the pure culture in the laboratory to the user of the cul- 

 ture, who was to prepare therefrom another culture to be used 

 for inoculating the soil. Careful investigation of this method 

 showed that its weakness lay in drying the cultures on the ab- 

 sorbent cotton, which frequently resulted in the death of the 

 organisms. More recently liquid cultures have been placed 

 on the market in this country, and these have, in the main, 

 proved to be more successful, notably those sent out by the 

 United States Department of Agriculture. 



Another very successful culture medium, now being used 

 by the Department of Plant Physiology at Cornel University, 

 is steamed soil. A soil, favorable to the development of 

 nodule organisms and usually a sandy loam, is sterilized by 

 steaming. It is then brought up to optimum moisture and 

 later inoculated with a number of different strains of B. 

 radicicola. After incubation for several days at a favorable 

 temperature, the soil cultures are ready for distribution. The 

 soil is sent out in small air-tight cans by parcel post. The 

 advantage of such a culture is that the organisms are viru- 

 lent and there is no danger from plant diseases or undesir- 

 able weeds. 



When a culture of this sort is received it may be used in a 

 number of different ways. It may be mixed with field soil 

 at the rate of 1 pound to 300 of the latter. This 300 pounds 

 of inoculated soil may then be spread on a acre of land in 

 the usual way. The culture may also be disposed of by the 

 glue method or it may be suspended in water and the extract 

 sprinkled on the seed and dried in the shade. In either case, 

 the seed should be sown as soon as possible. 



242. Resume. — The biological phases of the soil are so nu- 

 merous and far-reaching that it is obviously impossible in 

 summarizing their practical relationships to do more than call 



