SOIL INOCULATION 825 



although so far all the bacteria capable of inoculating leguminous 

 plants are classified under one species Bad. radicicola or Rhiz. legumino- 

 sarum, different morphological, serological, and cultural differences are 

 found between the forms inoculating different plants. Morphologically 

 they are differentiated by the formation of peritrichous or monotrichous 

 flagellation. Serologically and culturally they are differentiated into 

 a number of groups (3 to 11), the different representatives of each group 

 being capable of cross-inoculation. However, even one type of plant 

 may be inoculated by strains of the organism which possess certain dis- 

 tinct differences. 



It was found 28 that (1) different strains of bacteria used in inoculating 

 soybeans differ in their nitrogen-fixing efficiency; (2) different strains of 

 bacteria used for soybean inoculation differ in their power of producing 

 nodules on the roots of the plants, as shown by actual count both as to 

 number and size of nodules; (3) different varieties of beans differ in 

 their relative "susceptibility" of inoculation; (4) the efficiency of nitro- 

 gen fixation varies with the soil composition and reaction. There is 

 no difference in the morphology of the strains, but physiologically they 

 may be different. This raises anew the question of the value of inocula- 

 tion of soil, already inoculated, with vigorous strains of the organism. 



Importance of legume inoculation. The effect of inoculation upon the 

 growth of legumes depends to a large extent upon the physical and 

 chemical soil conditions, such as aeration, temperature, moisture, soil 

 composition, reaction, etc. 



The effect of legume inoculation was found to consist in increasing 

 the percentage of nitrogen in the tops and roots of the plants and the 

 percentage of ash (excluding phosphorus) in the tops. 29 Inoculation 

 alone increased 30 the yield of clover and alfalfa on a Colby silt loam 

 15.6 per cent; lime and inoculation gave an increase in yield of 49.7 

 per cent and in nitrogen content of 52.3 per cent. The addition of 

 phosphorus and potassium to this soil did not give any large increase 

 in yield. However, in the case of a poor soil, inoculation and lime, as 

 well as applications of phosphorus and potassium, gave marked increases 

 in crop yield; inoculation alone nearly doubled the crop yield, while 



2 « Wright, 1925 (p. 127). 



29 Amy, A. C, and Thatcher, R. W. The effect of different methods of in- 

 oculation on the yield and protein content of alfalfa and sweet clover. Jour. 

 Amer. Soc. Agron., 7: 172-185. 1915; 9: 127-137. 1917. 



30 Graul, E. B., and Fred, E. B. The value of lime and inoculation for alfalfa 

 and clover on acid soils. Wis. Agr. Exp. Sta., Res. Bui. 54. 1922. 



