SPECIAL CROPS. 25o 



Analyses also show the composition of soils, and are, in some 

 measure, a guide in adapting crops to the soil, but the expecta 

 tiou cherished, a few years ago, that chemistry would solve all 

 the difficulties of agriculture, has not been realized. There are 

 so many considerations besides the elements in the soil and 

 crops, that chemistry can only suggest what the farmer must 

 prove by practice. It is true that the intelligent farmer will 

 always he aided, by a knowledge of the principal elements of 

 the crops he cultivates, of the soils on which he cultivates them, 

 and of the manures applied, but the rain and the dew, the air 

 and the sunshine, which he cannot regulate, will often change 

 his best planned results. 



All soils contain mineral matter and phosphate of lime suffi- 

 cient for a crop of any kind ; but it is readily seen that if the 

 same crop is removed, year after year, and no equivalenl 

 returned, certain elements will become entirely exhausted. 

 But if the elements removed can bo replaced by manures, or 

 such a succession of crops raised that each element will be 

 taken in its turn, allowing the soil an interval of several years 

 to recuperate, the soil will retain its fertility. It is in this con- 

 nection that the analyses of manures are valuable, and here 

 that chemistry has done and is doing useful work for Agricul- 

 ture. We give below the principal elements of various 

 manures and fertilizers. 



A cord of leached ashes contains about 



147 pounds phosphoric acid, 184 pounds silex. 



41 " oxide of magnesia, 21 " oxide of iron, 



196 " magnesia, 50 " potash, 



1.057 " carbonic acid, 2,227 " lime. 



Average dung of a cow, for one year, contains 



4.800 pounds genie, 37 pounds chalk, 



677 " carbonate of ammonia, 24 " common salt, 



71 " bone dust, . 15 " sulphate of potash. 



37 " plaster. 



