16 SOILS OF THE EASTERN UNITED STATES. 



SUMMARY. 



The Marshall silt loam is the most extensive single soil type known 

 to exist in the United States. 



It possesses a dark-brown silty loam surface soil, underlain by a 

 yellow or mottled silty loam or silty clay subsoil. 



It constitutes the dominant brown prairie soil extending from west- 

 central Indiana across central and northern Illinois, northern Mis- 

 souri, southern Iowa, and through eastern and central Kansas and 

 Nebraska. 



It is derived from finely divided silty mineral material, primarily 

 of glacial origin, but distributed over its present locations largely 

 through the moving agency of the wind. This material is known as 

 the loess. 



Its surface is level to undulating or in some cases gently rolling. 



In altitude it extends from about 650 feet above sea level in Indiana 

 and Illinois to altitudes above 2,000 feet in the central and western 

 portions of Kansas and Nebraska. 



At present the Marshall silt loam is adequately drained through the 

 installation of thousands of miles of tile drains which have been used 

 to supplement the partially established natural drainage of the type, 

 particularly in eastern and central portions of its development. In 

 the more western areas its natural drainage is adequate. 



The Marshall silt loam lies chiefly within the humid region of the 

 temperate portion of the United States, although its western exten- 

 sion occupies a large portion of the dry-farming region of central and 

 western Kansas and Nebraska. This variation in rainfall condition, 

 attendant upon the wide extent of the type, constitutes the domi- 

 nant factor in the variation of its crop adaptations and yields. 



The Marshall silt loam, both in average yield per acre and in its 

 wide extent of territory, constitutes the dominant Indian-corn soil 

 of the central prairie States and of the United States. 



In addition, oats in the more eastern portion, wheat in the central 

 and western portion, and the cultivated grasses universally, consti- 

 tute important crops and the crop rotations generally adopted for 

 the type consist of several crops of corn followed by one of the small 

 grains, in turn succeeded by grass. 



Farther west, under dry-farming conditions, Kafir corn, milo maize, 

 broom corn, emmer, alfalfa, and durum wheat are produced. 



Special crops aside from these mentioned are not produced to any 

 extent upon the Marshall silt loam, owing principally to its high 

 value for the production of the general farm crops. 



Certain varieties of apples may be grown on the more rolling areas 

 of the Marshall silt loam. 



