PHYSICAL PROPERTIES OF SOILS 



21 



SOIL TYPES 



11. Crop Growth and Physical Properties. The pref- 

 erence of certain crops for particular kinds of soil, as 

 wheat for a clay subsoil, potatoes for a sandy soil, and 

 corn for a silt soil, is due mainly to the characteristic of 

 the crop in requiring a definite amount of water, and a 

 certain temperature 

 for growth. These 

 conditions are met 

 by the soil being 

 composed of various 

 grades of particles 

 which enable a cer- 

 tain amount of water 

 to be retained, and 

 the soil to properly 

 respond to heat and 

 cold. In considering 

 soil types, it should 

 be remembered that 

 there are so many 

 conditions influenc- 



FIG. 



First Centrifuge used in the Mechan- 

 ical Analysis of Soils. 



ing crop growth that 



the crop-producing 



power cannot always be determined by a mechanical 



analysis of the soil. The following types have been 



found to hold true in a large number of cases under 



average conditions, but they do not represent what 



