26 SOILS AND FERTILIZERS 



(i in Fig. n) there are from 30 to 50 per cent of clay 

 particles, mostly disintegrated limestone. The soil of 

 the Red River Valley of the North belongs to this class. 

 The surface soil contains from 7 to 10 per cent of 

 vegetable matter and the subsoil about 25 per cent of 

 limestone in a very fine state of division. For the pro- 

 duction of wheat, the subsoil should have a good store 

 of water. 



The second type of wheat soil (2 in Fig. n) has less 

 clay and more silt. Many prairie subsoils which pro- 

 duce good crops of wheat contain about 25 per cent of 

 sand, 50 per cent of silt, and from 1 8 to 25 per cent of 

 clay. Soils of this class when well stocked with moisture 

 in the spring produce good crops of wheat, but are not 

 able to withstand drought so well as soils of the first 

 class ; during wet seasons, however, the yields are larger 

 than on heavier clay soils. 



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

 those which are composed mainly of silt, containing 

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

 clay. The high pe-r 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 it 

 is essential that a good supply of organic matter be 

 maintained in such soils so as to bind together the soil 

 particles. The special peculiarities of the different 

 grain crops as to soil requirements are discussed in 

 connection with the food of crops. 



