FERTILITY AND HUMUS IN DRY AREAS 405 



doing under the best possible conditions" is welcome to 

 all the comfort he can get from making fertility a thing 

 so intangible. If the elements of fertility phosphate, 

 potash and lime are not a part of the soil, what are they 

 a part of? Humus in the discussion, of course, means 

 organic, that is, vegetable matter, whatever may be its 

 stage of decay. 



The soils are usually fertile. The richness of the 

 soils in dry areas in all the essential elements of plant 

 food is owing chiefly: (1) to the inherent richness of 

 the soil particles; (2) to the similarity of the subsoil to 

 the soil in its essential constituents ; (3) to the little loss 

 of fertility by leaching, and (4) to the extent to which 

 the soil has been moved by rodents. 



The richness of the soil particles is owing chiefly 

 to the source from which they have come (see p. 62). 

 This inherent richness applies largely to food that is 

 not yet available. This reserve food is unlocked grad- 

 ually by the cultivation given and through other 

 agencies, hence the ability of these soils to maintain an 

 undiminished production for a long term of years. 



It cannot be said, of course, that the subsoil is in 

 all instances similar to the surface soil, but in many 

 instances it is. Because of this the beneficial descent 

 and ascent of soil moisture is facilitated, the feeding 

 ground for the roots of plants is relatively enlarged and 

 the removal of plant food to the surface soil from below 

 is made very easy and sure. This explains why it is 

 possible to grow grain on lands for long periods which 

 increase rather than decrease in their producing power. 



On nearly all soils in dry areas the loss from leaching 

 is so small that it is not to be considered. The excep- 

 tions to this are rare. There is, therefore, virtually no 

 loss of fertility from this source, which is a never-end- 

 ing source, of loss in humid areas. This means that 

 inert fertility is made available slowly and that it is 



