THEORY OF SOIL FERTILITY 179 



pains ("Soil Fertility and Permanent Agri- 

 culture") to analyze the resources of the soil 

 of his state and to set down in definite figures 

 how many ordinary crops of corn may be 

 grown before the soil is mined empty. Be- 

 yond that time, which he numbers in years 

 encompassing only two or three generations, 

 the soil becomes merely a mixing bowl. It is 

 no longer innately fertile. Ultimately one 

 can imagine it as comparable to the beaker of 

 distilled water in which the scientist of to-day 

 experiments by adding just enough plant food 

 to grow a fixed crop. 



If a given acre will cease producing food 

 entirely, or even fall so low in productiveness 

 that the crop does not repay the labor ex- 

 pended thereon, such a condition must affect 

 the value of the land. And, in addition, if, to 

 keep that soil fertile, the husbandman must 

 feed the soil to make it feed him, again the 

 value of the land must be affected. To use a 

 far-fetched illustration, the mines of Newcastle 

 when empty of their virgin coal, and filled 

 again by carrying coals to Newcastle, would 

 be worth the market value of that coal, minus 

 what it cost to buy that coal in the first place 

 plus the cost of transportation. "Salting" a 



