1? 4 AGRICULTURAL ECONOMICS 



yet been worked out, but it is of importance in compensation and 

 valuation cases. 



Serious soil exhaustion did not arise under the old agricultural 

 conditions where people practically lived on the land and no great 

 amount of material had to be sold away from the land. Phosphate 

 exhaustion was the most serious occurrence, and as the original supplies 

 were not as a rule very great, it must have been acute by the end of 

 the eighteenth century in England, where remarkable improvements 

 were, and still are, effected all over the country by adding phosphates. 

 The crowding of the population into cities, and the enormous cheap- 

 ening of transport rates, led during the nineteenth century to the 

 adoption in new countries, particularly in North America, of what 

 is perhaps the most wasteful method of farming known continuous 

 arable cultivation without periodical spells of leguminous and grass 

 crops. The organic matter was rapidly oxidized away, leaching and 

 erosion increased considerably when the cover of vegetation was 

 removed, while the compound particles that had slowly been forming 

 through the ages soon broke down. Nothing was returned to the soil, 

 the grains and other portable products were sold and the straw burnt. 

 The result has been a rate of exhaustion unparalleled in older coun- 

 tries, and wholly beyond the farmer's power to remedy ; consequently 

 he left the land and moved on. The excellent experimental studies 

 of Hopkins at the Illinois Experiment Station, of Whitson at Wis- 

 consin, and other American investigators have shown that additions 

 of lime, of phosphates, and sometimes of potassium salts, with the 

 introduction of rotations, including grass and leguminous crops, 

 and proper cultivation, will slowly bring about a very marked 

 improvement. 



D. Topographical Limitations to Agriculture 



48. SOIL EROSION 1 

 BY R. O. E. DAVIS 



Destruction of the natural growth and clean cultivation on hilly 

 land, without protection against erosion, results in the removal of the 

 soil material by water more rapidly than it is formed and in a very 



1 Adapted from "Soil Erosion in the South,' 1 Bulletin 180, United States 

 Department of Agriculture, pp. 9-23. Part of the first paragraph is torrowed from 

 an article by the same author in Yearbook of the Department of Agriculture, 1913, 

 p. 208. 



