62 PRACTICAL FARM CHEMISTRY. 



the most of it exists in fixed combinations, and is 

 not immediately available, yet there is enough of it 

 thus ready for the use of plants, or becomes so in 

 the course of time, to produce the most luxuriant 

 plant growth year after year for a long period, per- 

 haps for generations. At first the crops are such as 

 not to be equalled on soils having been long in 

 cultivation even with heaviest manuring. Then 

 gradually the yields become smaller, as the avail- 

 able plant foods are removed from the soil, year 

 after year; and unless the stock is replenished, the 

 soil must after a while become exhausted, ''worn- 

 out," and unproductive. The reduced stock of the 

 plant foods is not rendered available any more as 

 fast as the plants need it for the production of pay- 

 ing crops. In place of the original soil, capable of 

 producing forty or fifty bushels of wheat to the acre, 

 and other crops in proportion, and all this without 

 the aid of costly applications of manures, we now 

 have a piece of land, that unaided, will give us a 

 yield of eight or ten bushels of wheat, and not more 

 than double that amount at best, provided we sup- 

 plement its natural stores with an additional five 

 or six dollars' worth of plant food. 



I have drawn this comparison for the purpose of 

 calling attention to the great value of the stores of 

 plant food in fertile soil. If we buy an acre of rich 

 land, we buy with it at least 20,000 pounds of nitro- 

 gen, 12,000 pounds of potash and 6,000 pounds of 

 phosphoric acid, which if we had to purchase it in 

 fertilizers at lowest whplesale rates, would cost us no 

 less than $2,000. Such soil, wherever found, is in 

 itself a rich mine, and worth money. The purchaser 

 can afford to pay $100 or $200 an acre for it much 

 better than ten or twenty dollars an acre for soil 



