■80 THE SOIL. 



potasli from the latter. Thus, by their contact with the 

 arable soil, they not only enrich it with ammonia, but 

 they effect, even in its minutest particles, a thorough 

 transposition of the nutritive substances required by 

 plants. 



The vegetable and animal remains m a soil seem to 

 exercise a remarkable influence upon the diffusion of 

 sihcates. The experiments made on this point show 

 that the absorptive power of an arable soil for sihcic 

 acid is in an inverse ratio to the amount of organic 

 remains in it ; so that a soil rich in such remains will, 

 when brought into contact \\dth a solution of sihcate of 

 potash, leave a certain amount of sihcic acid unabsorbed, 

 whereas an equal bulk of soil poor m organic remains 

 will take up the whole of the sHicic acid in the solution. 

 The incorporation of decaying vegetable and animal 

 matter will, therefore, in a soil containing disintegrable 

 sihcates, first of all accelerate the decomposition of the 

 sihcates, by the action of the carbonic acid generated in 

 the process of decay, and then, as these substances 

 diminish the absorptive power of the soil for silicic 

 acid, as soon as this acid has passed into solution, 

 it is distributed through the soil more widely than 

 would have been the case had these substances not been 

 present. 



On many fields poor in clay, the growth of grass for 

 several years will, in consequence of the organic matters 

 collecting in the soil, which serve to promote the distri- 

 bution of the silicic acid, act more favourably on a suc- 

 ceeding crop of a cereal plant than a plentifiil apphcation of 

 farm-yard manm^e, whose organic constituents, quite irre- 

 spective of the silicate of potash in the straw, are always 

 in operation to effect the same object. On many other 

 fields, especially on those abounding in lime, where there 



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