CHAPTER XXIII 



FIELD EXPERIMENTS IN THE SOUTH, INCLUDING SOUTHERN 



ILLINOIS 



THE gray silt loam on tight clay is one of the common types of 

 prairie land in the Kansan and lower Illinoisan glaciations. This 

 or very similar prairie soil is found in many places, as in south- 

 ern Illinois, northern Missouri, southern Iowa, and southeastern 

 Kansas. In Illinois this soil type is found chiefly between the 

 Kaskaskia and Wabash rivers in an area bounded on the south by 

 the Ozark Hills and on the north by the terminal moraine of the 

 Wisconsin glaciation, which passes through Shelby, southern Coles, 

 and Edgar counties. 



This type of soil is well known and everywhere recognized by the 

 farmers themselves as " hardpan land." It consists of a friable gray 

 silt loam which commonly varies in depth from 6 to 1 2 inches, and 

 below which is a light gray or nearly white layer, or stratum, of 

 slightly loamy silt varying from less than one inch to more than 10 

 inches in thickness, and commonly referred to as " the gray layer." 

 At a depth of 16 to 20 inches the soil is underlain by a tight clay 

 subsoil, frequently termed " hardpan." It should be understood, 

 however, that this subsoil is not true hardpan, which consists of 

 sand or gravel cemented together with clay to form a substance 

 which is practically impervious to water. 



The subsoil of this gray silt loam prairie is a tight clay, inclined 

 to be gummy. Water passes through it, although quite slowly, 

 and when wet it can be spaded without special difficulty, but when 

 dry it becomes stiff and hard. Closely related to this prairie soil 

 are level upland timbered soils underlain with tight clay, found 

 in the southern part of Indiana, Illinois, and Iowa, and also in 

 northern Missouri and western Kentucky. 



Where this soil is enriched by proper treatment, excellent crops 

 are grown in seasons of normal rainfall, but they are likely to suffer 

 in times of drouth more than would be the case with a better sub- 



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