TRANSFORMATION OF ORGANIC MATTER 687 



index of the availability of the nitrogen in the particular material, 

 especially in respect to the particular soil. 39 Different organic sub- 

 stances decompose with different rapidity. 40 



Attempts have been made to differentiate between the fertility 

 of different soils on the basis of the ammonia formed by a given quantity 

 of soil from a given amount of protein, either in solution or in soil. 

 When dried blood, cottonseed meal, urea or other organic material 

 with a high nitrogen content and, therefore, with a narrow C:N ratio 

 is added to normal soils, a large amount of nitrogen will accumulate 

 as ammonia. A number of investigations ("ammonification studies") 

 have been devoted to measuring this ammonia formed from an excess of 

 protein material in different soils. The solution method was at first 

 suggested. 41 A 0.5 to 5.0 per cent sterile peptone solution was inocu- 

 lated with a quantity of soil (usually 0.5 to 10 grams per 50 to 100 cc. 

 of solution) , incubated for 2 to 8 days, then the ammonia was determined 

 by distilling the solution with MgO. Certain differences were obtained 

 in the amount of ammonia formed in various soils. It was soon found, 42 

 however, that these differences may be due more to the difference in the 

 quantity of minerals introduced with the various soils rather than to 

 the differences in the kind or activity of the soil flora. It was then 

 suggested 43 to use a soil extract peptone solution, but this medium also 

 shows variations as a result of differences in the composition of the ex- 

 tract obtained from the various soils. Since the peptone is so rapidly de- 

 composed in solution and since all soils contain large numbers of bacteria 

 capable of forming ammonia from peptone, very little difference is 

 obtained between different soils. 



These limitations of the solution method led to the introduction of the 

 soil method (beaker or tumbler method). 44 The method consists in 



39 Lipman, J. G. Bacteriological methods for determining the available 

 nitrogen in fertilizers. Jour. Indus. Engin. Chem., 2: 146-148. 1910. 



40 Lohnis, F., and Green, H. H. Uber die Entstehung und die Zersetzung von 

 Humus, sowie tiber dessen Einwirkung auf die Stickstoff Assimilation. Centrbl. 

 Bakt. II, 40: 52-60. 1914. 



« Remy, 1902 (p. 710). 



42 Fischer, H. Uber die physiologische Wirkung von Bodenauszugen. 

 Centrbl. Bakt. II, 24: 62-74. 1909; Versuche uber Stickstoff umsetzung in 

 verschiedenen Boden. Landw. Jahrb., 41: 755-S22. 1911. 



43 Lohnis, F. Zur Methodik der bakteriologischen Bodenuntersuchung. 

 Centrbl. Bakt. II, 12: 262-267, 448-463. 1904; 14: 1-9. 1905. 



44 Vogel. Beitrage zur Methodik der bakteriologischen Bodenuntersuchung. 

 Centrbl. Bakt. II, 27: 593-605. 1910; Lipman, J. G. Chemical and bacterio- 

 logical factors in the ammonification of soil nitrogen. N. J. Agr. Exp. Sta. 

 27th Ann. Rpt. 1906, 119-187. 



