AGRICULTURAL CHEMISTRY. 



187 



This table shows, that, other things being supposed equal, a supply 

 of nitrogen sufficient for a full rye crop would answer but for one- 

 third of a clover or beet crop; the phosphoric acid sufficient for a 

 meadow is but little more than half enough for a wheat field, and 

 only one-third as much as a crop of beans requires. It appears that 

 the potash which would fully nourish a crop of wheat is nearly enough 

 for grass or beans; while for clover twice, and for beets four-and-a- 

 half times as much is needful. A clover crop demands almost ten 

 times as much lime and magnesia as suffices for rye, and a wheat crop 

 must have more than ten times as much silica as serves the growth 

 of an equal yield of beans. 



The erroneous conclusions which a hasty deduction might bring 

 out of the foregoing instructive table are checked by the fact ex- 

 pressed in the next proposition, viz: 



5. Different plants, from peculiarities in their structure, draw differ- 

 ently on the same stores of nutriment. 



There are some plants which flourish on the poorest soils, being 

 adapted to resist the extremes of drought, and accumulate their food 



