24 SOILS AND FERTILIZERS 



producing good crops of wheat, but are not able to 

 withstand drought so well as soils -of the first class. 



To the third class of wheat soils (3 in Fig. 10) belong 

 those which are composed mainly of silt, containing 

 usually 75 per cent., and from 10 to 15 per cent, of clay. 

 The high per cent, of fine silt gives the soil clay-like 

 properties. Soils of this class are adapted to a great 

 variety of crops. For the production of wheat on silt 

 soils it is very essential that a good supply of organic 

 matter be kept in the soil so as to bind together the 

 soil particles. The special peculiarities of the different 

 grain crops as to soil requirements will be considered 

 in connection with the food requirements of crops. 



17. Sandy, Clay, and Loam Soils. — In ordinary 

 agricultural literature the term 'sandy/ 'clay,' or 

 ' loam ' is used to designate the prevailing character of 

 the soil. Sandy soils usually contain 90 per cent, or 

 more of silica or chemically pure sand. The term 

 light sandy soil is sometimes used to indicate that the 

 soil is easily worked, while the term heavy clay 

 means that the soil offers great resistance to cultiva- 

 tion. Many soils which are clay-like in character are 

 not composed very largely of clay. There are sub- 

 soils in the western states which have clay-like char- 

 acteristics but contain only about 15 per cent, of clay, 

 the larger part of the soil being silt. A loam soil is a 

 mixture of sand and clay ; if clay predominates the 

 soil is a clay loam, while if sand predominates it is a 

 sandv loam. 



