46 BOARD OF AGRICULTURE. 



and a solution of plaster on soils benefited or not by plaster, that 

 in the former case potash and magnesia are liberated in consider- 

 able quanties ; in the latter not at all. Certain minerals which 

 contain silica, alumina, <fec., analogous to the composition of 

 soil, and which being formed under conditions analogous to the 

 composition of the soil, may be supposed to exist in the soil, 

 when subjected to the action of saline solution, undergo chemical 

 changes, which throw some light on this indirect action of fer- 

 tilizers. Minerals of this kind containing lime, subjected to a 

 solution of common salt, will part with the lime, and hold the 

 soda and salt in fixed combination. This new compound, treated 

 with a solution of potash, will lose a portion of its soda and 

 acquire potash. A solution of magnesia will displace the potash 

 again. And, in general, the effect of any one alkali in solution, 

 will be to displace a quantity of some other held in the combi- 

 nation. 



Thirdly, manures exert a physical effect on the soil. Peat 

 or vegetable matter will often act favorably on soil, by altering 

 the texture. The extremes of dryness or wetness in light or 

 heavy lands are brought by it to a proper medium, although 

 this is not its only action. 



The effect of lime on clay is physical to a great degree, as 

 was found by the Lusatian farmers in liming their clay lands 

 to bring them into tillable condition. They found that under- 

 draining produced the same effect. Lime is found, when mixed 

 with moist clay, to increase its bulk and change its texture. 



Nearly all fertilizers when applied in large quantities, as 

 stable manure, ashes, &c., produce greater or less alterations 

 in the texture of the soil which are advantageous. 



These three modes of action are all dependent one on another, 

 and each fertilizer exerts them all to a greater or less degree. 

 It may happen that many fertilizers which act chiefly to supply 

 food to the plant, in other cases may act by improving the 

 texture of the soil. On many rich soils stable manure does 

 more good by the physical action of the litter than it does by 

 the fertilizing materials which it adds. 



The action of manures is influenced by the peculiarities of 

 the soil. Some soils are benefited by plaster and salt, while 

 others are indifferent to these fertilizers ; it is probable that the 

 testimony of practical men, asserting that some soils are dam- 



