10 SOILS OF THE EASTERN UNITED STATES. 



steeply sloping soil, there is considerable variation in these different 

 localities with regard to the extent to which it is occupied for agri- 

 cultural purposes. In the former areas, as in Kentucky, southern 

 Indiana, Iowa, Wisconsin, and some portions of Missouri, probably 

 80 per cent of the type has been cleared of its natural hardwood 

 timber growth and occupied for the production of farm crops. In 

 the cases where the t} 7 pe is only developed along the bluffs and steeper 

 portions of the counties where it occurs, probably not more than 15 

 per cent of its extent has been cleared of forest and used for the pro- 

 duction of tilled crops. The remainder of the type in such locations 

 is used as the farm woodlot and to a considerable degree for pastur- 

 age purposes in the feeding of beef cattle and the grazing of dairy 

 stock. There is thus considerable variation in the occupation of the 

 type, dependent upon its topographic features. 



There are some portions of the type at one time cleared and occu- 

 pied for agricultural purposes which have latterly been allowed to 

 revert to pasturage or to partly forested conditions because of the 

 development of excessive erosion. These areas are localized in 

 extent and are of no great size when compared with the total 

 extent of the type in the States where it occurs. They merely 

 mark the desire of certain communities to extend the areas of culti- 

 vated land beyond the natural limits set by the slope and rainfall 

 conditions which control erosion. In Nebraska there are still con- 

 siderable areas of the Knox silt loam possessing a gently rolling to 

 slightly hilly surface configuration, which, owing to rainfall condi- 

 tions, are occupied by native prairie grasses, either pastured off or cut 

 as wild hay. These areas are rapidly being occupied for the produc- 

 tion of Kafir corn, emmer, and alfalfa, and it is probable that within 

 the next few years all of the areas of the Knox silt loam topographi- 

 cally suited for agricultural purposes will thus be occupied. 



CROP ADAPTATIONS. 



The texture, structure, and general physical characteristics of the 

 Knox silt loam limit its crop adaptations to the production of corn, 

 the small grains, and grass in all except very restricted areas. 



Its climatic surroundings vary somewhat the selection of those 

 crops which will best be suited to the conditions of temperature and of 

 rainfall locally prevalent. 



Thus corn constitutes the dominant crop upon the tilled areas of 

 the Knox silt loam in both Illinois and Nebraska. The yields se- 

 cured are high, ranging from 40 to 45 bushels per acre on the average. 

 However, the acreage devoted to corn is limited, principally by 

 topographic conditions, although in the more western localities the 

 somewhat scanty rainfall not infrequently tends to decrease the 



