THE KNOX SILT LOAM. 5 



chiefly covered by native pasture grasses or, more recently, by seeding 

 to the cultivated grasses in the regions where this portion of the type 

 is agriculturally occupied. 



There is a wide range in the altitudes at which the Knox silt loam 

 is found. Along the Ohio River and along the Mississippi, near 

 the mouth of the Missouri, the altitude of its surface ranges from 

 500 to 650 feet above tide, or from 50 to 150 feet above adjoining 

 river bottoms. In central Indiana and Illinois its altitude is usually 

 from 750 to 900 feet above tide level, with the same general relation- 

 ship to the streams as already described. In Wisconsin, Iowa, and 

 Nebraska, as well as in western Missouri, its altitude ranges from 

 1,000 to 1,300 feet above tide level, and from 100 to 150 feet above 

 the major streams. 



The type is found in the temperate region of the United States 

 extending from about 37 north latitude to 44 north latitude in 

 the Mississippi River region and along its principal tributaries. 

 The range in climatic surroundings, from its most southern occur- 

 rence in Union County, Ky., to the most northern region where it 

 has been mapped in the Viroqua area, Wisconsin, is considerable, 

 and has its effect upon the crop adaptation and the common uses of 

 the soil. The limitation from north to south is principally one of 

 temperature. There is a corresponding variation in the rainfall 

 conditions attendant upon the type from a rainfall of nearly 40 

 inches in the Indiana and Illinois sections to a rainfall of about 25 

 inches in eastern Nebraska. This also effects the crop adaptations 

 of the type, and somewhat varies the farm practice over its culti- 

 vated area. 



In general, the drainage of the type is adequate, especially upon 

 all of the more rolling and hilly portions of its development. There 

 are areas, however, in the gently rolling upland where minor depres- 

 sions, to some extent, lack adequate natural drainage, and in such 

 depressions the crops are normally below the average for the type 

 and for the region, indicating the necessity for supplementing the 

 natural conditions with artificial drainage systems. 



Erosion, however, is the principal difficulty to be experienced in 

 the management of this soil. In all those areas where it' occurs, 

 principally, along the river bluffs and in the adjoining rolling to hilly 

 territory it is most desirable to leave the type in timber or to estab- 

 lish natural pasturage over areas which have already been cleared. 

 Even in the regions of low rainfall where the Knox silt loam occurs, 

 it is decidedly susceptible to erosion when its surface is left ex- 

 posed, especially after planting to the intertilled crops. In general, 

 it would be better to omit cultivation over all such areas, using them 

 for forestry and pasturage purposes and confining cultivation to the 

 more level portion of the type or to other soils upon the upland. 



