30 SOILS 



provided these stiff soils have been well aerated by tillage 

 tools, for a time sufficient to put the soil in good physical 

 condition. The best types of wheat land carry less 

 moisture from 12 to 15 per cent. than the best grass 

 types. 



Many secondary types are found. While the me- 

 chanical analysis of soils recognizes but eight divisions, 

 classified from the size of soil grains, the direct applica- 

 tion to the field will show a great many more factors, since 

 other considerations are in effect here, as the humus 

 content, the arrangement of soil grains, the lay of the 

 land, the ancestry of the soil, and the climatic help or 

 hurt. 



The force of this is shown where humus is added to a 

 soil. You find two soils alike in every way. Add humus 

 to one the texture is changed, the water-holding capac- 

 ity is increased, the productivity is made greater. You 

 have not changed the size of the soil grains, the basal 

 principle of type remains the same. 



Another example : Take two sand soils, of the same 

 basal type precisely, the components in both instances 

 being the same. One is located in a section where the 

 rainfall is abundant and where it is frequent. The other 

 soil in a section where just the opposite extremes exist. It 

 follows, without discussion, that other conditions being 

 present food, warmth, seed, and culture the moist soil 

 will generally produce a satisfactory crop and the dry 

 soil an unremunerative crop. 



Mechanical analysis a help and guide. We receive 

 assistance when we know soil types, for we have a most 

 helpful guide here at hand. But we have no posi- 

 tive rule to follow in the selection of crops we shall grow. 

 With more study, with more investigation, we may in 

 future years predict with greater safety the behavior of 



