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fertility of that soil (provided it be done with judgment) 

 quite as well as leaving it at rest or fallow. 



In practical farming-, one crop in artificial rotation 

 with others, extracts from the soil a certain quantity of 

 necessary inorganic matters ; a second carries off, in 

 preference, those which the former had left, and neither 

 could nor would take up. 



Experience proves that wheat should not be attempt- 

 ed to be raised after wheat on the same soil; for, like 

 tobacco, it exhausts the soil. But if decaying 

 vegetable mattter, gives it the power of producing 

 how happens it that, in soils formed in large proportion 

 of mouldered wood, the corn-stalk attain no strength, 

 and droops permanently? The cause is this; the 

 strength of the stalk is due to silicate of potash, and the 

 corn requires phosphate of magnesia; neither of which 

 substances a soil of decaying vegetable matter can afford, 

 since it does not contain them : the plant may, indeed, 

 under such circumstances, become an herb, but it will 

 bear no seeds. We say phosphate of magnesia is neces- 

 sary ; — the small quantities of the phosphates found in 

 peas and beans is the cause of their comparatively small 

 value as articles of nourishment, since they surpass ail 

 other vegetable food in the quantity of nitrogen they 

 contain. But as the component parts of bone, namely, 

 phosphate of lime and magnesia, are absent in beans 

 and peas, they satisfy appetite without increasing thte 

 strength. 



Again, how does it happen that wheat does not flour 

 ish on a sandy soil, and that a limestone soil is also un- 

 suitable, unless mixed with a considerable quantity of 

 clay ? Evidently because these soils do not contain po- 

 tash and soda, (always found in clay ;) the growth of 

 wheat being arrested by this circumstance, even should 

 all other requisite substances be presented in abundance. 

 It is because they are mutually prejudicial by appropri- 

 ating the alkalies of the soil, that wormwood will not 

 thrive where wheat has grown, nor wheat where worm- 

 wood has been. 



One hundred parts of wheat straw yield 15 1-2 of 



