TILLAGE 287 



lying subsoil or rock. Frost action is also responsible for 

 many landslides. 



River-bottom Erosion. Good valley land is often destroyed, 

 either by the wearing away of the river banks along the main 

 channel or by the gouging out of new channels. The Kansas 

 River flood, of 1903, for example, completely destroyed 10,000 

 acres of excellent farming land and caused a total loss of at 

 least $22,000,000. 



PREVENTION OF EROSION 



Prevention in General. Since surface run-off is primarily the 

 cause of soil erosion, its prevention and control depend, in a large 

 measure, upon the way in which the protective cover of trees, 

 grass and other vegetation is cared for, and on the way in 

 which cleared and cultivated lands are handled. There are, of 

 course, some factors influencing surface run-off that are beyond 

 the control of man, such as the distribution of the rainfall and the 

 geological formation. Other factors, like the slope and the character 

 of the soil, may be modified to a certain extent. 



Much can be done to decrease and prevent erosion by prevent- 

 ing fires from sweeping through forests and over cut-over lands, 

 by ceasing to overgraze the ranges, and by ceasing to clear steep 

 slopes for farming. Since so many lands devoted to agriculture 

 are rolling, erosion becomes a common agricultural problem. 

 The following discussion concerns the control of erosion in farming. 



Drainage and Organic Matter. Surface run-off may be 

 lessened by good underdrainage. In this way the capacity of a 

 soil for taking in water is increased. Often the thorough drainage 

 of a large body of peat greatly lessens the amount of flood water 

 that will flow away because the greater portion, if not all, of the 

 rainfall would be absorbed by the soil. 



When the organic matter of any heavy soil is increased the 

 soil becomes more open and crummy in structure, thus increasing 

 its water-absorbing capacity. This also results in decreasing 

 the surface run-off. 



Tillage. Plowing loosens the soil and this allows the rain 

 water to soak more readily into the ground. In this manner deep 

 hillside plowing of a heavy soil especially lessens erosion to a 

 considerable extent. 



When a hillside is plowed, it should be done at right angles 

 to the slope; and all cultivated crops should be planted so that 



