24 SOILS 



average gives rise to a grade distinguished by the name of 

 the material there present in excess of that normal aver- 

 age. Hence, we get names that stand for the particular 

 type, as sand soils, where much sand is present ; clay 

 soils, where much clay or silt is present ; and humus soils, 

 where much organic matter is present. 



Plants show preference for certain soils. And there 

 is a very great problem unfolded here, for the most of 

 our field crops do not do equally well on each of these soil 

 types. Not a little partiality is shown. While some crops 

 are not so very choice of their soil homes, others are par- 



A CROP THAT IS HARD ON THE SOIL 



Tobacco is usually a profitable crop, but one that quickly exhausts the soil 

 of its fertility 



ticularly mindful ; in fact, some, like the grape or tobacco 

 plant, permit their fancy to extend even as far as the 

 manufactured product. 



Size of soil particles. It is due to the size of the parti- 

 cles of which soils are made that we have our various 

 classes of sand and silt and clay rock descendants. 

 When these particles are separated mechanically, we find 



