6 SOILS OF THE EASTERN UNITED STATES. 



soil is undertaken when the moisture content is neither too great 

 nor too small. One of the most fundamental requisites for the 

 improvement of crop yields upon this soil and for the extension 

 of its profitable use lies hi the addition of organic matter to the sur- 

 face soil through the employment of stable manures and of green 

 crops plowed under. 



Over considerable areas of the Clarksville silt loam tile under- 

 drainage will be requisite, in order to bring the subsoil drainage 

 into condition more favorable for the production of large yields of 

 the staple crops. The efficacy of such drainage is adequately dis- 

 played by the crop yields which are reported from areas of the Clarks- 

 ville silt loam which are underlain at a depth of 24 to 30 inches by 

 a porous layer of broken chert nodules. This layer, which is found 

 extensively in the western Kentucky and western Tennessee counties 

 of which soil surveys have been made, very materially assists in the 

 subsoil drainage of the type, and it is from areas thus underlain that 

 the highest crop yields are habitually reported. If the same efficient 

 underdrainage could be secured through the installation of tile 

 drains in many other areas occupied by the type the increase hi 

 crop yields would be sufficient to pay for the total cost of the installa- 

 tion within a brief period after the tile were laid. 



To a limited extent, certain areas of the Clarksville silt loam 

 require protection from erosion. In general, however, this is not a 

 serious difficulty with the type except in its marginal portions. The 

 usual methods of allowing the steeper slopes to remain seeded to 

 grass or allowing them to be occupied by forest growth will usually 

 prove adequate. In certain areas where the occupation of all of 

 the area of the type for agricultural purposes is desirable contour 

 farming and terracing may be employed. 



One of the greatest difficulties encountered in the management 

 of the Clarksville silt loam is that of plowing and tilling the type 

 when the moisture condition of both surface soil and subsoil is such 

 that the earth may be turned and broken to plow depth without 

 the clodding of the surface soil and the puddling of the subsoil 

 where the plow sole runs over it. If the surface soil be plowed when 

 only a little too moist it is liable to turn over in a long continuous 

 strip of unbroken soil, which later on would naturally be harrowed 

 into corn-pact clods of little value for the production of a crop. When 

 the surface soil is hi this condition the subsoil will also be so wet 

 that the passage of the plow over it will compact and harden a layer 

 at plow depth, giving rise to the so-called "hardpan" or plow-sole 

 layer. Land plowed in this condition is not only difficult to handle 

 in all the subsequent tillage operations, but there is also established 

 an impenetrable zone between the surface soil and subsoil through 

 which the roots of the growing crops may not pass. The "hardpan " 



