MATTERS TO BE RESTORED VARY. 261 



clay-soil), in wliicli the proportion of lime or magnesia in 

 the soil does not exceed that of phosphoric acid, and 

 where provision must "be made for replacing the former 

 as well as the latter. Again, there are milhons of acres 

 of fertile land, which, like calcareous soils in general, 

 are exceedingly poor in potash, and become absolutely 

 barren without a proper supply of this ingredient. 



There are, on the other hand, miUions of acres of 

 fertile fields abounding so richly in nitrogen that any 

 additional supply of that element would be mere waste. 



Ashes will not promote the growth of clover on fields 

 abounding in potash, whilst the appHcation of manuring 

 agents containing phosphoric acid will have that effect ; 

 on the other hand, ashes ^vill make clover grow on land 

 deficient in potash, where bone-earth proves useless ; and 

 a simple supply of Hme containing magnesia will often 

 suffice to restore the productiveness for clover where the 

 land is deficient hi hme and magnesia. 



When a farmer, besides corn and flesh, grows and sells 

 other produce, the nature of the required supply of 

 mineral elements is thereby necessarily altered. In the 

 average potato produce of three hectares of land we 

 take away the seed-constituents of four wheat crops, 

 besides about 600 lbs. of potash, and in the average 

 turnip produce of three hectares the seed-constituents of 

 four wheat-crops, besides about 1000 lbs. of potash. A 

 supply of phosphoric acid alone will not suffice, in this 

 case, to keep up the productiveness of the land. 



The grower of commercial plants, such as tobacco, 

 hemp, flax, the vine, &c., must in like manner strictly 

 attend to the law of restitution, which, properly inter- 

 preted, does not imply that he should bestow the same 

 anxious care upon the replacement of all constituents 

 ahke which ' have been taken away in the crops. It 



