512 



PRINCIPLES OF SOIL MICROBIOLOGY 



without any additional carbohydrate. The substances rich in nitro- 

 gen allowed an accumulation of almost 50 per cent of the nitrogen as 

 ammonia, but this was considerably reduced when additional available 

 energy in the form of carbohydrates was added. 



Table 49 illustrates the formation of ammonia from different organic 

 materials when sufficient non-nitrogenous organic matter (starch) is 

 added so as to introduce the same amount of fresh undecomposed 

 organic matter. In these studies, the various amounts of the organic 

 materials were added to 100 gram portions of soil and the ammonia 

 determined after 9 days. 9 When the accumulation of ammonia from 

 the various nitrogenous substances is compared, it is found to be, with 

 the exception of casein, in direct relation to the nitrogen content of 



TABLE 49 

 Per cent of organic nitrogen transformed into ammonia in soil 



SOURCE OF NITROGEN 



Casein 



Dried blood 



Soybean cake . . . 

 Cottonseed meal 

 Linseed meal . . . 



NITROGEN 



CONTENT 



per cent 



12.40 

 13.29 



8.28 

 5.10 

 5.00 



1 GRAM OF 

 EACH ORGANIC 



MATERIAL 



ADDED TO 100 



GRAMS SOIL 



NHs-N 



mgm. 



50.2 

 42.4 

 40.9 

 27.1 

 26.0 



132.9 MGM. 

 ORGANIC NITRO- 

 GEN PLUS 

 ENOUGH STARCH 

 TO MAKE 

 EQUIVALENT 

 AMOUNTS OF 

 CARBON 



NH3-N 



mgm. 

 31.4 

 18.9 

 34.1 

 34.0 

 34.1 



the materials. When the same amount of nitrogen is added to the 

 soil, the amount of ammonia accumulated depends upon the concen- 

 tration of carbonaceous substances present. These may serve as 

 sources of energy for the microorganisms, so that less of the protein is 

 decomposed and more of the nitrogen used up by the organisms for 

 the synthesis of their protoplasm. When enough starch is added to 

 make the amount of carbon equal in all cases, the amount of ammonia 

 accumulated will generally be constant. When the amount of nitrogen 

 is very high as in the case of dried blood, the amount of starch added 

 was very large; since this is a very readily available source of carbon, 



9 Kelley, W. P. The biochemical decomposition of nitrogenous substances in 

 soils. Hawaii Agr. Exp. Sta. Bui. 39. 1915. 



