PREVENTION OF EEOSION BY TERRACING. 3 



ascribed the difficulty often encountered in convincing the landowner 

 that destructive erosion is taking place on his farm. 



In some sections of the United States, particularly in the South, 

 erosion is assisted materially by the alternate freezing and thawing 

 of saturated soil. (PI. II, fig. 2.) The freezing process upheaves a 

 thin layer of the soil near the surface. As this layer of loosened soil 

 thaws, it settles, with a tendency to move slightly down the slope. 

 It is very common for heavy rains to occur directly after the thaw- 

 ing period and wash away the loosened soil from the surface of the 

 field. Probably no other combination of natural conditions could 

 operate more effectually to rob a field of its most fertile soil in the 

 same period of time. 



METHODS OF PREVENTING EROSION. 



Erosion is due chiefly to the free movement of water over the sur- 

 face of the land, which carries off partiples of soil. If all rain water 

 were absorbed by the ground upon which it falls, soil erosion would 

 be reduced to a minimum. It is obvious, therefore, that in order to 

 prevent or reduce erosive action the soil must receive treatment that 

 is conducive to the admission and the storage of large quantities of 

 rain water; and methods must be employed to reduce the velocity, 

 and thereby the transporting power, of the run-off water. 



Since the storage capacity of a soil depends upon its porosity, any 

 treatment which results in an increased porosity of the soil will re- 

 duce erosion materially. This porous condition usually is obtained 

 directly by deep plowing and bj^ a thorough incorporation of organic 

 matter in the soil. Methods of subsurface drainage which lower the 

 ground water level imi^rove the porous structure of the soil and in- 

 crease its ability to absorb surface water. The treatment of cover, 

 such as seeding land to pasture, growing timber, and planting cover 

 crops in the winter, tends to check and diminish erosion greatly. 

 Other methods \vhich retard the flow of the water and conduct the 

 excessive run-off from the field with a reduced amount of erosion, 

 are contour plowing, hillside ditching, and terracing. 



It is the purpose of this paper to deal primarily with the preven- 

 tion of erosion by means of terracing ; but since all of the methods of 

 prevention enumerated above tend to mitigate the destructive effects 

 of erosion, some of them should be used invariably in connection with 

 terrace systems. The manner in which each contributes to the pre- 

 vention of erosive action will be described briefly. 



DEEP TILLAGE AND APPLICATION OF HUMUS. 



By deep plowing the absorptive power and reservoir capacity of a 

 soil is increased greatly. It is said ^ that 10 inches of loose, plowed 



1 Soil Report N. 3, Illinois Agricultural Expeciment Station, p. 16. 



