ESTIMATION OF FOOD IN A AVIIEAT SOIL. lit) 



been determined by chemical anal3^sis, and are not li3q^o- 

 tbetical. It is therefore certain tliat a wlieat crop draws 

 from the ground half as much again of phosphoric acid 

 and sihcic acid, and one- third more potash, than a rye 

 cro]). 



The supposition that a wheat soil, to the depth of 10 

 inches, contains in physical combination 0-05G per cent. 

 of phosphoric acid, 0*034 per cent, of potash, and 0-34 

 per cent, of sihcic acid, which makes a hundred times as 

 much as a wdieat crop would take in corn and straw from 

 the field, is purely hypothetical ; and the present question 

 is to determine the limits up to which this estimate may 

 be accepted as true. 



If arable soil is left for twenty-four hours in contact 

 with cold muriatic acid, a certain quantity of potash, 

 phosphoric acid, silicic acid, as well as lime, magnesia, &c. 

 is extracted. If the soil is treated for a long time with 

 boiling muriatic acid, the quantities of dissolved sihcic 

 acid and potash are much greater. Lastly, by decom- 

 posing by fusion the silicates, and then treating with hot 

 muriatic acid, we can obtain all the potash and sihcic 

 acid contained in the soil. Without risk of error we may 

 assume that those nutritive substances which can be ex- 

 tracted by cold muriatic acid are most feebly retained by 

 the soil, and approach nearest the elements in physical 

 combination ; or, at all events, so near, that by the 

 common disintegrating agencies they very easily pass into 

 this form of combination. 



In this way Dr. Zoeller subjected to analysis two 

 kinds of wheat soil — tlie loam of Bogenhausen and of 

 Weihenstephan, the latter of which in particular repre- 

 sents an excellent wheat soil. One hundred parts of 

 these two soils yielded to cold muriatic acid — 



