24:0 THE SYSTEM OF FARM- YARD MANURING. 



supplying to their land potash, lime, magnesia, or silicic 

 acid, and that salts of ammonia and superphosphate of 

 lime will suffice to restore the productiveness of all 

 exhausted fields. 



A farmer may, therefore, be quite justified in con- 

 sidering that his field can never grow poorer in potash 

 because he never takes any from it, or that it actually 

 contains a superabundance of potash since every rota- 

 tion tends to accumulate in the soil a fresh amount of 

 that ingredient ; but it is childish of him to think him- 

 self justified by this circumstance in assuring another 

 agriculturist, about whose system of cultivation he 

 knows nothing, that the fields of the latter equally con- 

 tain a superabundance of potash. 



There are millions of acres of fertile land (sand and 

 clay-soil), in which 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 millions 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, millions 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 application of manur- 

 ing agents containing phosphoric acid will have that 

 effect ; on the other hand, ashes will make clover grow 

 on land deficient in potash, where bone-earth proves 

 useless ; and a simple supply of lime containing mag- 

 nesia will often suffice to restore the productiveness for 

 clover where the land is deficient in lime and mag- 

 nesia. 



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 Ibs. of potash, and in the average 



