164 THE SOILS AND CROPS OF THE FARM. 



been shown that, in the ordinary prairie drift soil, a 

 large proportion of the roots are between two and 

 five inches deep at a point where they are likely to be 

 disturbed by cultivation, and that by far the larger 

 portion of these are between two and four inches deep. 



It has also been clearly demonstrated that, by cut- 

 ting off these roots to the depth of four inches, at six 

 inches from the center of the hill the yield of corn 

 is decreased in a marked degree. The decrease in 

 yield may vary from one- eighth to one- third the crop, 

 and a decrease of one- sixth to one-fourth the crop 

 may be expected. 



Cultivating with an ordinary cultivator does not 

 prune the roots so completely as may be done by di- 

 rect methods, so that as much injury from deep culti- 

 vation as from root pruning need not be expected, but 

 that the injury is often considerable has been shown 

 in many places. The following table shows the aver- 

 age yield of corn during three years at the Illinois 

 Experiment Station from deep and shallow cultiva- 

 ted plats, and from a plat receiving no cultivation 

 after the corn was planted but having the weeds re- 

 moved by scraping the surface with a hoe: 



Av. bu. 

 Kind of Cultivation. ^ per acre 



dur.3 yrs 



Shallow, average 3 plats 82 



Deep, average 3 plats 74 



None, one plat 79 



The practice of shallow cultivation is becoming 

 much more common than formerly, machinery having 

 been perfected for this purpose, and now many farm- 

 ers never cultivate their corn over two inches deep. 



Stirring a soil dries out the portion that is stirred 



