112 



fere with its capability of yielding remunerative 

 harvests. 



Liebig, in his " Natural Laws of Husbandry," 

 says with regard to this subject: 



" A manure will exercise its beneficial action upon a 

 field in the most marked manner, when it establishes a 

 more suitable relative proportion between the several 

 mineral constituents in the soil, because upon this propor- 

 tion the crops are dependent. No special argument is 

 needed to demonstrate that where a wheat soil contains 

 just so much phosphoric acid and potash as will suffice 

 to afford the quantity of these two substances required for 

 a full wheat crop, and no more (accordingly for every part 

 by weight of phosphoric acid, two parts by weight of 

 potash), any additional supply of one-half more, or even 

 of double the quantity of potash, cannot exercise the 

 slightest possible influence upon the crop of corn. The 

 wheat-plant requires for . its full development a certain 

 relative proportion of both nutritive substances, and any 

 increase of one beyond this proportion makes the other not 

 a whit more effective, because the additional supply 

 exercises by itself no action. 



" An increase of phosphoric acid alone has just as little 

 influence in making the returns greater, as an increase of 

 potash alone : this law applies equally to every nutritive 

 substance potash, magnesia, and silicic acid ; no supply 

 of these substances beyond the requirement of the wheat- 

 plant, or its capacity of absorption, will have any effect 

 upon its growth. The relative proportions of the mineral 

 substances which the plants draw from the soil, are easily 

 determined by analyzing the ashes of the produce. It is 

 found by analyses that wheat, potatoes, oats, and clover 



