74 CULTURE OF FARM CROPS. 



others also, for an all but indefinite period. In the other 

 case that in which the produce is kept up by means of 

 the import of cattle food or artificial manure, or of part 

 one and part the other the loss of the constituents in 

 question, derived from the soil itself, will, of course, be by 

 so much less than the amounts assumed above, and that of 

 others will be also reduced. There can indeed be little 

 doubt that, in actual practice, the loss to the soil itself, by 

 the sale of corn and meat, is generally more nearly one 

 half, and frequently less than one half, of the above assumed 

 amounts of the constituents mentioned ; and that of others 

 will be less accordingly. 



" So far as the purchase of food for stock was relied upon, 

 no selection could well be made from the 'current supplies 

 in the market, that would not bring upon the farm more 

 of the mineral constituents than the increase of produce 

 due to the manure obtained from it would receive from the 

 land in the form of corn and meat. In fact, to increase 

 the sales of corn and meat, by the import of cattle food, as 

 generally practised, is to increase, and not to diminish, the 

 amount of available mineral constituents within the soil. 

 If, on the other hand, the produce were kept up by means 

 of artificial manures, the rules of selection among intelli- 

 gent practical men are such, that almost invariably much 

 more of phosphoric acid, at any rate, would be brought 

 upon the land, than would be removed from it in the increase 

 of corn and meat due to the use of the imported manures. 



" In the case supposed, without import, it is probable that, 

 in the majority of instances, phosphoric acid would be the 

 most liable to become deficient in relation to other consti- 

 tuents. The sources of phosphoric acid developed in recent 

 years, promise, however, to answer to any demand that seems 

 likely to be made upon them to remedy such exhaustion of 

 it as the present agricultural practices of the country induce. 



" In the case of imports, on the other hand, especially 

 where they consisted chiefly of the current artificial manures 

 rather than of cattle foods, potass would be the most likely 

 to become deficient. The sources of potass in the market 



