PREVENTION OF EROSION BY TERRACING. a 
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 particles 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 by a thorough incorporation of organic 
matter in the soil. Methods of subsurface drainage which lower the 
ground water level improve 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 which 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 
1Soil Report N. 8, Dllinois Agricultural Experiment Station, p. 16. 
