322 MICROBIOLOGY OF SOIL 



nitrogen. Older humus has, therefore, a narrower carbon-nitrogen 

 ratio than humus of recent origin. The former is more resistant to 

 decay, however, than new humus. In a concrete way, on the other 

 hand, it may be stated that fresh vegetable material of a narrow car- 

 bon-nitrogen ratio will decay more rapidly than fresh vegetable material 

 of a wide carbon-nitrogen ratio. The reverse, nevertheless is true of 

 vegetable materials in advanced stages of decay. Under any given 

 climatic conditions and in any given soil type, the carbon-nitrogen 

 , ratio may give important indications only as to the availability of the 

 humus nitrogen. Lawes and Gilbert, as quoted by Hall, found the 

 following carbon-nitrogen ratio in the organic matter of different soils: 



■Cereal roots and stubble 43 ■ o 



Leguminous stubble 23.0 



Dung 18.0 



Very old grass land 13.7 



Manitoba prairie soils 13.0 



Pasture recently laid down 11 . 7 



Arable soil 10. i 



Clay subsoil 6.0 



Hall concludes, therefore, that humus with a wide carbon-nitrogeri 

 ratio is' more valuable than humus with a narrow carbon-nitrogen ratio, 

 since the latter will be attacked more easily by the soil bacteria. Brown 

 and Allison indicate that there might be a possibility of applying ma- 

 terials of a wide carbon-nitrogen ratio to supply the deficiencies of 

 organic matter on the basis that the former may have the same or 

 better effect on bacterial activities such as azofication, or non-symbiotic 

 nitrogen fixation. 



The Transformation of Nitrogen Compounds 



Ammonification. Experimental Study. — By ammonification is 

 meant the production of ammonia by bacteria out of protein substances 

 or their cleavage products. That ammonia production in the soil is 

 a -biological process was first demonstrated by Miintz and Coudon in 

 1893. These investigators showed that no ammonia is formed in sterile 

 soils. They also showed that ammonia may be produced out of nitro- 

 genous organic matter by molds as well as by bacteria. Marchal not 

 only confirmed these observations, but proved that various micro- 

 organisms differ markedly in their ability to produce ammonia. Of 

 the several species of bacteria tested by him, B. mycoides (one of the 



