Soils and Soil Management 55 



may be considered as a condition of the subsoil rather 

 than as a different material, where it is composed 

 of the same material as the subsoil. 



88. Sand. Sand is broken-up fragments of a mineral 

 called quartz, or flint. It often occurs mixed with con- 

 siderable quantities of coarse gravel. Pure white sand 

 is almost valueless for agricultural purposes, because it 

 supplies no needed mineral element. However, it rarely 

 occurs pure, but mixed with other minerals that supply 

 plant food. Sandy soils are usually classed as "light" 

 soils because of the light draft in plowing. They are in 

 reality very heavy, for a cubic foot of air-dry sand will 

 weigh over a hundred pounds, whereas an equal quan- 

 tity of clay will weigh only about eighty pounds. The 

 grains of sand are rounded, and so there are spaces be- 

 tween them. This allows water and gases to move easily 

 through sandy soils. Because of their open nature, sandy 

 soils readily take in large quantities of water. For the 

 same reason, they allow it to drain off or evaporate 

 quickly. Sandy soils are usually drier and better aerated, 

 and will, for this reason, warm up sooner than other 

 soils and are, hence, preferred for growing early vege- 

 tables. 



89. Clay, in an agricultural sense, includes any soil 

 composed largely of very fine particles, which gives the 

 land a close, compact, adhesive nature. Clay, as used 

 by chemists and potters, refers to the disintegrated mass 

 of certain kinds of rocks. The several kinds of clay soils 

 vary widely in chemical composition, physical proper- 

 ties, and fertility. Usually, however, clay soils are very 

 productive. Clay has the property of absorbing large 

 quantities of water, often as much as from 50 to 75 

 per cent of' its own weight. Even the dry clay road 



