CHAPTER XXIII 

 PERMANENT AGRICULTURE 



The land in the United States of America has been called 

 the " floor space of the nation." The work for three hun- 

 dred years has been to occupy this floor space. Forests 

 have been cut down, swamps have been drained, and 

 streams have been spread out to furnish moisture for fields 

 in places where little came from the clouds. 



So long as there was new land to occupy, — rich fields 

 awaiting the plow, — there was food in plenty and to spare. 

 Now, however, there is little new land to occupy, and the 

 number of mouths that must be fed continues to increase. 



Land can no longer be abused and then thrown back 

 upon a generous Nature to repair the waste of man. 



The soil has been compared to money in the savings 

 bank, upon which the interest only may be drawn each 

 year. If more than this is wanted, we begin to draw upon 

 the principal. That is to say, a certain amount of plant 

 food — nitrogen, phosphorus, potassium, etc. — is un- 

 locked each year by the rain, the frost and the unseen or- 

 ganisms of the soil. 



Certain plants take out more of a given element than 

 do others. While clover, for example, is taking out a 

 great deal of potash, the store of nitrogen in the soil is 

 increasing ; and when com later begins to draw upon the 

 nitrogen, the drain upon the potassium is lessened. 



It is definitely known just how much of each element 

 is taken out of the soil by each crop. It therefore 



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