130 



SOILS. 



decay progresses on the lower surface, but active animal 

 agencies (see below) carry the organic remnants bodily down. 

 But where heavy clay soils prevail, these animal agencies are 

 much restricted by the compactness of the material; only a 

 light surface-layer of mold would be formed, and the humus 

 of the lower soil layers must of necessity be derived from the 

 decay of the roots only. This origin is claimed by Kosticheff 1 

 for the high content of black humus in the tchernozem or 

 black earth of Russia. Following Hellriegel in determining 

 the weight of roots contained in successive equal layers of soil 

 from the surface downwards, Kosticheff gives for each six 

 inches the following data as found in the tchernozem, taking as 

 100 the root-content of the surface layer: 



It will be seen that there is a very close correspondence of the humus 

 content with the root development in the several layers, and it seems 

 as if though but little of the humus could be derived from the surface 

 growth, which is that of the grasses of the steppe. 



The climate of the black-earth country of Russia is, though not 

 properly arid, yet one of rather deficient and uncertain rainfall. But as a 

 consequence of extremely arid conditions, and in sandy lands, it may 

 even happen that the immediate surface soil contains /ess humus than 

 what, in the farmers' habitual parlance, would be called the subsoil ; 

 because of the penetration of slow combustion for some distance into 

 the porous soils. It will then be lower down that, in the presence of a 

 favorable degree of moisture and lower temperature, the conditions of 

 normal humification are fulfilled. 



1 Abstract in Ann. de la Science Agronomique, Tome 2, 1887. 



