52 THE MECHANICAL ANALYSIS OF SOILS [chap. 



The following table gives the results of the determi- 

 nation of carbon, nitrogen, humus, and the percentage 

 of nitrogen in the humus, in a selection of extremely 

 rich virgin soils obtained from different parts of the 

 world ; the Canadian, Russian, and Monte Video soils 

 were very similar uniform fine-grained grey or black 

 soils found on the great plains : 



Locality. 



1. Canada 



2. Canada 



3. Russia . 



4. Rhodesia 



5. Monte Video 



6. New Zealand 



Indian Head 



Wide Awake 



Ploty 



Salisbury 



( 



Tararua 



Mountains 



Description of 

 Soil. 



Black Prairie 



Black Steppe 



Black Vlei 



Black \ 



"Camp" Soil J 



Black Sandy 



Pasture 





2-59 



2-58 



2-19 



20-15 



1-89 

 12-66 







o-3i7 

 o-33o 

 c-268 

 1-89 



0-261 

 0-949 



o 



I? 



02 



4-07 

 2-71 

 2-42 

 2-40 



3-5i 



4-67 



These results would seem to indicate that the most 

 valuable humus, i.e., that which will decay rapidly 

 and yield nitrogen compounds available as food for 

 plants, is that possessing a high ratio of carbon to 

 nitrogen. 



Against this, Berthelot and Andre have investigated 

 the ratio of carbon to nitrogen in the different portions 

 of the humus which can be dissolved by alkalis or acids, 

 and they find that the most soluble portions contain the 

 highest proportion of nitrogen. It does not, however, 

 follow that the substances most soluble in acids or 

 alkalis are necessarily those which will most readily be 

 converted by bacteria into a form available for plants, 

 and, on the whole, the evidence seems to show that a 

 humus rich in nitrogen will yield it very slowly to crops. 



Humus acts as a weak cement and holds together 



