374 A NATIONAL PLAN FOR AMERICAN FORESTRY 



EROSION OF AGRICULTURAL LANDS 



Soil surveys recently made in the Central States by various State 

 agencies have revealed some 17 million acres of badly eroded agri- 

 cultural land on which the continuance of agriculture is at least doubt- 

 ful under present conditions. Of this total something like 6 or 7 

 million acres lies in the upper Mississippi River drainage. On these 

 lands farm abandonment is progressing. 



The widespread occurrence of erosion is indicated by figure 8, based 

 on data of the Illinois Soil Survey, which shows the extent and dis- 

 tribution of lands "destructively" and " seriously " eroded in Illinois. 

 The field work which this map represents included sampling of every 

 10 acres. " Destructively eroded" areas are defined by Dr. A. E. 

 Norton, assistant chief of the Illinois State Soil Survey, as "areas 

 which cannot be cultivated by any practical known means at a profit 

 because they erode faster than it is possible to build up the soil. 

 * * *. Within this division there are areas suitable for pasturing, 

 orcharding, and timbering. The percentage of the first two is rela- 

 tively small in comparison with that suitable for timbering only." 

 Dr. Norton defines "seriously eroded" lands as "areas which can 

 be cultivated by specialized methods for profit. Certain treatment, 

 such as terracing and the application of readily available organic 

 matter, must be given the land before it can be cultivated. No 

 doubt much of it could best be utilized in forests until such time as 

 there is a greater demand for cultivated crops than at present." The 

 Illinois Soil Survey recognizes a third class of eroded land: Harm- 

 fully eroded areas are subject to sheet erosion. Unless the methods 

 of agriculture are changed in the future, "this area will some day 

 fall in the destructive erosion division." Land of this class is not 

 indicated on the map. The survey data show some 3 million acres 

 of destructively eroding land, 3 million acres of seriously eroding land, 

 and 12} million acres of harmfully eroded land. 



State soils specialists and State foresters have estimated that be- 

 tween 50 and 75 percent of the more severely eroded land in the upper 

 Mississippi River basin has already been abandoned. Much of this 

 land is almost completely denuded. 



According to the results of investigations made by the Missouri 

 Agricultural Experiment Station on loamy soils continuously in corn, 

 a 7-inch layer of soil is removed in 49 years from tilled land that slopes 

 4 feet in 100. This is at the rate of 20.5 tons of soil per acre per year. 

 It is possible that even greater soil losses have occurred on areas of 

 loess soil such as those in southern Illinois. 



In the driftless area, dairying has been extensively developed. 

 There is every reason to believe that it has been overdeveloped. Too 

 much land has been cleared, too large an area has been put into crops 

 and pasture, too much trampling has taken place. Consequently 

 gullying is making it impossible for the industry to continue on its 

 present scale. Although only about one third of the total area 

 cleared is being cultivated, areas under cultivation include much land 

 with grades exceeding 20 percent and occasional slopes with grades 

 of 35 percent. On such slopes erosion, if once started, proceeds 

 rapidly. In Europe, slopes with grades of more than 15 percent are 

 considered unsuitable for cropping. In this country the same belief 

 has long been held by foresters and is coming to be entertained by 

 agriculturists and soils experts. 



