grass. This thinning of the grass cover subjects these lands 

 to changes which reduce absorption and infiltration and 

 to waste by erosion in the same manner as do fires fol- 

 lowing deforestation. 



In the predominantly grass-covered West North Central 

 States (Minnesota, North Dakota, South Dakota, Iowa, 

 Nebraska, Missouri, and Kansas) and in such Mountain 

 States as Montana, many millions of acres have been converted 

 to tilled land during the past 20 years many of them to the 

 especially ruinous "dry-farming" of cereal crops. In view 

 of conventional agricultural practices and the greater sus- 

 ceptibility of clean-tilled, single-crop land to erosion than 

 grassland, this increase in the proportion of crop lands has had 

 significant unfavorable influence from the point of view of 

 conservation of soil and of water. 



[d\ TREATMENT OF STREAMS. 



Streams also have been treated in a manner which hastens 

 the flow of unused waters to the sea. Many creeks and 

 small headwater rivers have been dredged and straightened 

 to carry off rapidly the waters fed by drainage ditches, and 

 the channels of great rivers have been straightened, deep- 

 ened and confined to promote navigation, to open fertile 

 flood plains to agriculture, and to reduce flood dangers. 

 The writer can recall a small river of his youth that was 

 25 to 30 feet across; today it is a straightened cleared ditch 

 barely 8 or 10 feet in width. 4 On this point Aldo Leopold, 

 noted scientist, has written as follows: 



I have just returned from Germany, and I am much impressed by the 

 almost nation-wide error which has been made there in straightening 

 small streams. The prevention of stream straightening by engineers 

 stands out in my mind as one of the imperative pieces of work, and 

 of course the development of any sound policy must probably be preceded 

 by considerable research. 5 



From the point of view of absorption, infiltration, re- 

 tardation of run-off, and maintenance of the groundwater 

 store, Nature's arrangements in respect to streams were 



4 Shiawasee River, Livingston County, Mich. 

 6 Madison, Wis.; letter of Nov. 21, 1935. 



57288 36 3 



