826 PRINCIPLES OF SOIL MICROBIOLOGY 



CaC0 3 , in addition to inoculation, brought about an increase in yield 

 of 182.8 per cent. Inoculation usually increased the percentage of nitro- 

 gen in the roots. Alfalfa showed an average gain of 87.5 pounds of 

 nitrogen on a poor soil and only 41.3 pounds on a rich soil; soybeans 

 properly inoculated fixed about 108 pounds of nitrogen in an acid soil 

 and about 129 pounds when half enough lime needed to neutralize the 

 soil acidity was added. 



The use of pure cultures affords a quick and easy method for intro- 

 ducing the bacteria which enable the leguminous plants to obtain nitro- 

 gen from the atmosphere. Fresh inoculation of soil with specific nodule 

 bacteria may be of direct benefit to the crop, even if the same plant has 

 been grown previously. 31 This is due to the fact that the organisms 

 present in the soil itself may not be as vigorous as freshly introduced 

 cultures and the small expense involved by fresh inoculation may be 

 fully compensated by the more vigorous growth of the plants. 



Nobbe and Richter found that in some cases 93 to 96 per cent of the 

 nitrogen in vetch was obtained from the atmosphere. The addition of 

 available nitrogen to the soil brought about a decrease in the amount of 

 nitrogen fixed. A fixation of 92 per cent of nitrogen in the alfalfa plants 

 as a result of inoculation was recorded. 32 Others 33 obtained a fixation 

 of 15 pounds of nitrogen for alfalfa with soil as an inoculum and 35 pounds 

 when a commercial culture was used for inoculation. In cylinder 

 experiments with various legumes turned under as green manures, in a 

 rotation of corn, potatoes, oats and rye, a gain of 54 pounds of nitrogen 

 annually over a period of seven years, as a result of inoculation, was 

 reported. 34 



Clover was found to contain at maturity an average of 27 per cent of 

 its nitrogen in the roots; 46 per cent of the total nitrogen of alfalfa was 

 also found in the roots. 35 



The nitrogen content of clover and especially of alfalfa inoculated 

 with the proper bacteria is greatly increased as a result of inoculation. 



31 Fred, E. B., and Bryan, O. C. The effect of nodule bacteria on the yield 

 and nitrogen content of canning peas. Soil Sci., 14: 413-415. 1922. 



32 Alway, F. J., and Pinckney, R. M. The nitrogen content of inoculated and 

 uninoculated alfalfa plants. Neb. Agr. Exp. Sta. 25th Ann. Rpt. 1912, 5G. 



33 Lipman, J. G. Tests of commercial cultures for soil inoculation. N. J. 

 Agr. Exp. Sta. Bui. 227. 1910. 



34 Lipman, J. G., and Blair, A. W. The yield and nitrogen content of soy- 

 beans as affected by inoculation. Soil Sci., 1: 579. 1916. 



36 Brown, P. E., and Stalling, J. H. Inoculated legumes as nitrogenous 

 fertilizers. Soil Sci., 12: 365-307. 1921. 



