RESTORATION OF FERTILITY. 147 



Thus we are in a position to give to the most sterile soil a state 

 of the greatest fertility for all plants, if we furnish to it the con- 

 stituents which they require for their growth. It would, indeed, 

 neither repay the labor nor the expense to render fertile on those 

 principles an absolutely sterile soil. But in our ordinary arable 

 soils, which contain already many of these constituents, it suffices 

 to supply the absent ingredients, or to increase those which are in 

 deficient quantity. At the same time, by the art of farming, the 

 soil must be put into a proper physical state, by which it is ren- 

 dered accessible to moisture and to rain, and is fitted to enable 

 the plants to appropriate these ingredients of the soil. 



Different genera of plants require for their growth and perfect 

 maturity, either the same inorganic means of nourishment, al- 

 though in unequal quantities and at different times, or they re- 

 quire different mineral ingredients. It is owing to the difference 

 of the food necessary for the growth of plants, and which must 

 be furnished by the soil, that different kinds of plants exert mutual 

 injury when growing together, and that others, on the contrary, 

 grow together with great luxuriance. 



Very little difference is observed in the composition of the ashea 

 of the same plants, even although they have grown on different 

 soils. Silica and potash form invariable constituents in the straw 

 of the Graminece ; and, in their seeds, there is always present 

 phosphate of potash and phosphate of magnesia. A large quan- 

 tity of lime occurs in the straw of peas and in clover. We know, 

 further, that in certain kinds of plants, the potash is replaced by 

 soda, and the lime by magnesia. 



It has been shown by the experiments of Boussingault,* that 

 the five following crops grown in succession on an equal surface 

 of the same field once manured, removed from the soil : — 



Ingredients of the soU. 



1 Year crop of Potatoes (tubers without herb) - - 2168 lbs. 



2 " " Wheat (straw and corn) - 3710 " 



3 " " Clover G200 " 



4 « « CWheatf 48S-0 " 



I Fallow Turnips 10SS " 



4 " " Oats (corn and straw) • - - - 21 5 " 



* Annales de Chimie et de Physique, t. i , p. 242 

 f On a system of alternate crops. 



