O T A'G R I C U L T U R E . 161 



arc the same in all plants, these vary in different 

 varieties of vegetation. 



As one kind of plant takes up one mineral from 

 the soil, and others take other kinds, the farmer finds 

 it advantageous to cultivate in succession different 

 varieties of plants on the same grounds j this is- 

 called rotation of crops. 



If a soil yields good crops of one vegetable, and 

 not of another, it must be wanting in the mineral 

 elements of the latter, which should be supplied. 

 If any particular plant, cultivated or wild, nourishes 

 in any given spot, an examination or analysis of the 

 ashes indicates at once the capabilities of the soil by 

 showing what soluble salts it furnishes. 



Decaying- vegetable and animal matters, when 

 applied to crops, act not only in supplying carbonic 

 acid and ammonia, but by furnishing such mineral 

 salts as are contained in them, and that, too, in the 

 very best condition to be taken up by plants. Hence 

 for any particular crop there is no manure so good as 

 the same kind of vegetable in a state of decay, or its 

 ashes, or the droppings of animals fed upon it ; but 

 in the latter case it is of the first importance to make 

 use of the whole manure of the animal, as its liquid 

 excretions, the part most liable to be lost, are by far 

 the richest in soluble salts. 



Nature seems to have made it a fixed law that if 

 one of the important ingredients of the plant is 

 absent, the others, though they may be present iii 

 sufficient quantities, cannot be used. This, if the soil 

 is deficient in alkalies, and still has sufficient quanti- 

 ties of all the other ingredients, the plant cannot 

 take these ingredients, because alkalies are necessary 

 to its growth. 



