162 ALTERNATION OF CROPS. 



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4. All plants do not restore to the soil either the 

 same quantity or quality of manure. 



" 5. All plants do not feed the soil equally." 



And from these principles he deduces the following 

 conclusions : — 



"1. That, however well prepared a soil may be, it 

 cannot nourish a long succession of crops without being 

 exhausted. 



"2. Each harvest empoverishes the soil to a certain 

 extent, depending upon the degree of nourishment which 

 it restores to the earth. 



"3. The cultivation of spindle roots ought to succeed 

 that of running and superficial roots. 



"4. It is necessary to avoid returning too soon to the 

 cultivation of the same, or to analogous kinds of vegeta- 

 bles, in the same soil. 



"5. It is very unwise to allow two kinds of plants, 

 which admit of the ready growth of weeds among them, 

 to be raised in succession. 



"6. Those plants that derive their principal support 

 from the soil, should not be sown, except when the soil 

 is sufficiently provided with manure. 



" 7. When the soil exhibits symptoms of exhaustion, 

 from successive harvests, the cultivation of those plants 

 that restore most to the soil must be resorted to. 



" These principles are confirmed by experience ; they 

 form the basis of a system of agriculture, rich in its pro- 

 ducts, but more rich in its economy, by the diminution 

 of the usual quantity of labor and manure. All cultiva- 

 tors ought to be governed by them ; but their apphcation 

 must be modified by the nature of soils and climates, and 

 the particular wants of each locality." — Chemistry applied 

 to Agriculture, 



