830 



PRINCIPLES OF SOIL MICROBIOLOGY 



various soil microorganisms, especially the bacteria and actinomyces, 

 with the result that the nitrogen is becoming available for higher plants. 

 It is this group of phenomena which brought about confusion in an 

 attempt to explain why the addition of available carbohydrates at first 

 lowers crop yield, 42 and why favorable results are obtained one year 

 after the application of carbohydrates, as shown in the following 

 summary : 



In various studies no effect has been noted as a result of application of 

 carbohydrates and, in some cases, even an injurious effect has been 

 observed. This may be due to the variability of the method for deter- 

 mining the total nitrogen. The following example may be taken as an 

 illustration: The addition of five tons of a pure carbohydrate (on a 

 water-free basis), whether in the form of straw, hay, plant stubble, green 

 manure, etc., is quite a large amount to add per acre of soil. Even 

 assuming that such a quantity is added and that it is all utilized by 

 the nitrogen-fixing bacteria as a source of energy (which is again doubt- 

 ful), the maximum amount of nitrogen fixed under these conditions 

 would be 0.5 part of nitrogen for every 100 parts of carbohydrate, or 

 50 pounds of nitrogen per acre. If the soil contains only 0.1 per cent 

 nitrogen, this will form only about 2\ per cent of the nitrogen content of 

 the soil, i.e., less than the error involved in the method for determining- 

 nitrogen. By using 5 gm. of soil for total nitrogen determination, the 

 difference will be only \ of a milligram. Those familiar with the method 

 know how easily such an error is obtained. 



The question of soil reaction has been also discussed in detail else- 



42 Kr tiger, W., and Schneidewind, W. Ursache und Bedeutung der Salpeter- 

 Zersetzung im Boden. Landw. Jahrb., 29: 747-770. 1900; Gerlach, M., and 

 Vogel, I. Versuche mit stickstoffbindenden Bakterien. Centrbl. Bakt. II, 

 9: 817, S80. 1902; 10: 636-643. 1903; Lipman, J. G. Soil inoculations with 

 Azotobacter beijerincki. N. J. Agr. Exp. Sta. 21 Ann. Rep. 1908, 144-147. 



43 Koch, Litzendorff, Krull and Alves, 1907-1909 (p. 586). 



