MANURES. 259 



their power of rendering the earthy ingredients of the soil more 

 soluble, or in any way more available to the roots of plants ; for 

 it happens in almost every instance that the solvent effect is pro- 

 duced by the action of materials which also come under the head 

 of nutrient manures. 



If there is any single fertilizer which is a solvent, and only a 

 solvent, it is common salt. This contains, it is true, only ele- 

 ments (chlorine and sodium) which are found in the ashes of nearly 

 all cultivated plants, and which are more or less important to their 

 growth ; but the amount of either of these that is absolutely 

 requisite to the perfection of the growth of any crop is so slight, 

 and the quantity of each that is to be found in every cultivated 

 soil is so great, that it would be fair to assume that crops can 

 always obtain from the natural source all of either chlorine 

 or sodium that they require. The marked action which generally 

 follows the use of small dressings of salt — say from 5 to 8 bushels 

 per acre — and the exceptional action in those cases where it seems 

 to be almost as active as Peruvian guano itself, indicate that it 

 exerts an influence on vegetation which can by no means be 

 ascribed to its supply of food directly to the plant. The manner 

 in which it is supposed to act as a dissolving agent is very well 

 described in the following quotation from Liebig's last work : — * 



"When the exhaustion of a field is not caused by the absolute 

 " deficiency of food elements, when even a more than adequate 

 *' supply of all the needful nutriment is there, but not in the pro- 

 *' per form, and where Consequently fallowing will again render 

 *' the crop remunerative, the farmer has means at his disposal to 

 *' assist the action of the natural agencies, whereby the conversion 

 " of the food into the state of physical combination is effected", 

 *' and thus to shorten the fallowing season, or even, in many in- 

 " stances, to make it altogether superfluous. 



" We have seen that the diffusion of earthy phosphates through 

 *' the soil is effected exclusively by water, which, if containing a 

 *' certain amount of carbonic acid, dissolves these earthy salts. 



* The Natural Laws of Husbandry. J. Von Liebig, Munich, March, 1S63. 



