494 THE PRINCIPLES OF SOIL MANAGEMENT 



most fertile portion; second, by such changes in the 

 physical condition of the land as greatly interferes with 

 all cultural operations. This is especially true where 

 large gullies are formed, as happens on some soil types, 

 or where ridges and mounds are formed by wind action. 

 In some sections and on certain classes of soil, wind 

 erosion is most serious; notably in dry regions of high 

 winds. Under other conditions, erosion by water is 

 most serious. 



350. Erosion by water. This type of erosion is a 

 function of flowing water. It therefore occurs almost 

 entirely on sloping land. The exception is where the 

 soil is underlain by a stratum of fine sand which flows 

 with the water when saturated. The removal of sand 

 below permits the soil to cave down. As has been noted 

 in another connection, erosion is greatly increased by 

 material carried by the water and which becomes its 

 tool. Some of the most effective practices for the con- 

 trol of this type of erosion are: (1) Deep plowing on 

 heavy soil, by which a larger part of the rainfall is 

 absorbed and retained. (2) Increased granulation of 

 the soil, which may be produced by the means explained 

 on page 104. The absorptive power and water capacity 

 of the soil is thereby increased so that there is a less 

 amount to flow away. (3) Addition of organic matter, 

 which not only aids granulation, but binds the soil 

 together. It also increases the water capacity of the 

 soil. (4) Underdrainage reduces erosion where the soil 

 is saturated with water. Instead of its flowing away 

 violently in rills, it is gradually removed in the drainage 

 channels, which are not subject to erosion. (5) Various 



