SOIL TYPES 19 



preference 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 peculiari- 

 ties of the crop in requiring definite amounts of water, 

 and a certain temperature for growth. These condi- 

 tions are met by the soil being composed of various 

 grades of particles wmich enable a certain amount of 

 water to be retained, and the soil to properly respond 

 to the influences of heat and cold. In considering 

 soil types, it should be remembered that there are so 

 many conditions influencing crop growth that the 

 crop-prodiicing 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 thev do not 

 represent what might be true of a case under special 

 conditions. For example a sandy soil of good fer- 

 tility in which the bottom water is only a few feet 

 from the surface, may produce larger grainc rops_than 

 a clay soil in which the bottom w r ater is at a greater 

 depth. In judging the character of a soil, special 

 conditions must alw r ays be taken into consideration. 

 In discussing the following soil types, a normal supply 

 of plant food and an average rainfall are assumed in 

 all cases. 



12. Potato and Early Truck Soils. — The better 

 types of potato soils are those which contain about 60 

 percent, of medium sand, 20 to 25 percent, of silt, and 



