496 THE PRINCIPLES OF SOIL MANAGEMENT 



it thrives, blue grass is permitted to occupy those areas 

 of the hillside most subject to erosion. Trees afford a 

 similar protection and are valuable in reclaiming eroded 

 land. It is a general custom to retain in some cover- 

 crop those steep areas of land most subject to erosion. 



(6) Contour farming, that is, the performance of all 

 tillage operations around the hill at a uniform level, 

 instead of up and down the slope, creates a succession 

 of small ridges which hold the water, to a certain extent. 



(7) Side-hill ditches are employed where contour farm- 

 ing does not create sufficiently large ridges to hold the 

 water. The two are usually combined. These side-hill 

 ditches are usually given a small grade along the face 

 of the slope, to gradually carry away the water. (8) 

 Terracing is preferred in some sections as a method to 

 prevent erosion as well as to facilitate tillage. The water 

 is, of course, held on each level strip throughout the suc- 

 cession of terraces. Where gullies have already formed, 

 there extension may usually be prevented by filling with 

 some porous material, such as straw, brush or stone, which 

 checks the flow of water and accumulates the sediment. 

 Cross-embankments are also useful. When these are 

 combined with the growth of grass, trees or other plants, 

 to bind the soil together and further protect it, such 

 land can frequently be reclaimed. 



351. Erosion by wind. Erosion by wind, including 

 the drifting of sand, may be checked by means of: 

 (1) Windbreaks, and in some cases, by keeping the sur- 

 face rough. (2) A surface covering such as stone or 

 vegetation, the latter to bind the soil together and 

 break the force of the wind. (3) The addition of organic 



