126 CHYMISTRY APPLIED TO AGRICULTURE. 



1st. That however well prepared a soil may be, it can- 

 not nourish a long succession of crops without becoming 

 exhausted. 



2d. Each harvest impoverishes the soil to a certain ex- 

 tent, depending upon the degree of nourishment which it 

 restores to the earth. 



3d. The cultivation of spindle roots ought to succeed 

 that of running and superficial roots. 



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

 cultivation of the same or of analogous kinds of vegetables, 

 in the same soil.* 



5th. 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. 



6th. Those plants that derive their principal support 

 from the soil should not be sown, excepting when the soil is 

 sufficiently provided with manure. 



7th. 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 prod- 

 ucts, but more rich in its economy, by the diminution of 

 the usual quantity of labor and manure. All cultivators 

 ought to be governed by them, but their application must be 

 modified by the nature of soils and climates, and the par- 

 ticular wants of each locality. 



To prescribe a series of successive and various harvests, 

 without paying any regard to the difference of soils, would 

 be to commit a great error, and to condemn the system of 

 cropping in the eyes of those agriculturists, who are too 

 little enlightened to think of introducing into their grounds 

 the requisite changes. 



Clover and sainfoin are placed amongst the vegetables 



* In addition to the reasons I have given why plants of the same or 

 analogous kinds should not be cultivated in succession upon the same 

 soil, there is another which I will here assign. M. Olivier, member 

 of the French Institute, has described with much care all the insects 

 which devour the neck of the roots of grain ; these multiply infinitely, 

 if the same or analogous kinds of plants be presented to the soil for 

 several successive years ; but perish for want of food, whenever plants 

 not suited to be food for their larvsB, are made to succeed the grains. 

 These insects belong to the family of Tipulae, or to that of flies. — 

 (Sixteenth Vol. of the Memoirs of the Royal and Central Agricultural 

 Society of Paris.) 



