114 



crops stated above, but that it is deficient in the proper 

 proportion of silicic acid containing, for example, for 

 1 part by weight of phosphoric acid, only 2J parts of 

 silicic acid, in an available condition this deficiency 

 will, in the first place, be felt in the crops of cereal plants, 

 whilst the potato and clover crops, on the contrary, will 

 not be at all diminished. It will depend upon the weather 

 to determine whether this deficiency in the crop of cereal 

 plants extends both to corn and straw, or is confined to 

 the straw alone. A want of potash, in proportion to all 

 the other constituents, will barely affect the wheat and 

 oat crops, but it will reduce the potato crop ; in like 

 manner, a want of lime and magnesia will impair the 

 clover crop. 



" If the ground can furnish one-tenth more potash, 

 lime, magnesia, and silicic acid than corresponds to the 

 given proportion of phosphoric acid thus, if 



Phosphoric Lime and Silicic 



Acid. Potash. Magnesia. Acid. 



Instead of 1 2'5 1-5 3-0 



The ground should be 



able to famish 1 2*75 1-65 3-3 



the crops would not turn out larger than before. But 

 if, in such a field, the quantity of phosphoric acid is 

 increased, the produce will increase, until the right 

 proportion is restored between the phosphoric acid and 

 the other mineral constituents. 



" The additional supply of phosphoric acid serves in 

 this case to increase the amount of potash, lime, and 

 silicic acid in the produce ; but if this additional supply 

 exceeds one-tenth of the phosphoric acid present in the 

 soil, the quantity in excess remains ineffective. Up to 

 this limit, every pound nay, every ounce of phosphoric 

 acid supplied, has, in this case, a fully determinate action. 



