SOIL INOCULATION 821 



secured with these pure cultures by Nobbe and others 11 were not con- 

 firmed by investigators both in America 12 and in Europe, 13 who found soil 

 to be superior to artificial cultures for inoculation purpose. The in- 

 oculating value of some of these earlier preparations has been com- 

 pared critically with the inoculating value of soil on which the 

 particular legumes were grown. 14 



Use of soil for inoculation of legumes. Nodule production on plants 

 is a result of chance contact; a large number of nodule-forming bac- 

 teria must, therefore, be present in the soil so that maximum nodule 

 formation may take place. After the first experiments on the inocula- 

 tion of legumes, it was found that certain crops, like clover, peas and 

 beans, did not benefit from inoculation; others, like alfalfa and soybeans, 

 could not be grown successfully without inoculation of the soil with 

 some soil in which these crops had been grown previously. It became 

 a common practice to top dress fresh soil with some old soil for these 

 crops. In most cases 300 to 500 pounds of soil, taken from the upper 6 

 inches of a field where the particular legume had been grown successfully, 

 was spread over each acre of soil and disked or harrowed in before the 

 planting of the seed. It was found 15 that soils once inoculated for soy- 

 beans and red clover did not need to be reinoculated when these crops 

 were again grown in the four-year rotation. Dry soil stored for thirty 

 months was as good for purposes of inoculation as fresh soil from the 

 field. Further studies 16 have shown that there is a considerable improve- 

 ment in the growth of peas in an acid silt loam, in which peas had grown 

 eleven years previously, as a result of inoculation with artificial cultures. 

 An acid soil may lead to a disappearance of certain nodule bacteria, the 

 destruction of the bacteria running parallel with increasing acidity. 

 The nodule bacteria survived for fifteen years in soils which were limed, 



11 Edwards, S. F., and Barlow, B. Legume bacteria. Ont. Dept. Agr. Bui. 

 164. 1908. 



12 Stevens, F. L., and Temple, J. C. The efficiency of pure culture inocula- 

 tion for legumes. N. C. Agr. Exp. Sta. 30th Ann. Rept., 48-57. 1908. 



13 Barthel, C. Culture experiments with bacterial inoculations of lupine and 

 alfalfa. Meddel. Centralanst. Forsoksv. Jordbruk., 95. 1914; K. Landbr. 

 Akad. Handb. o. tdskr., 53: 251-280. 1914. 



14 Feilitzen, H. V. Nitro-Bacterine, Nitragin oder Impferde? Centrbl. 

 Bakt. II, 23: 374-378. 1909. 



16 Albrecht, W. A. Viable legume bacteria in sun dried soil. Jour. Amer. 

 Soc. Agron., 14: 49-51. 1922; Mo. Agr. Exp. Sta. Bui. 197. 1922. 



14 Whiting, A. L. The relation of inoculation to quality and yield of peas. 

 Jour. Amer. Soc. Agr., 17: 474-487. 1925. 



