Natural Fertility of the Soil 15 



and J cent a pound for the phosphoric acid and potash. 

 The labor in raising the crop, the expense of harvesting 

 and putting it upon the market, and the profit, must 

 come out of the difference between what is paid and what 

 is received. Naturally, as the ratio between the con- 

 stituents contained in the products sold and the price 

 received is increased, the rate of income to a unit of ex- 

 haustion is increased, though in many cases the increased 

 cost of the labor necessary is in proportion to the increased 

 price received. This may be illustrated by a comparison 

 on the fertility basis of the sale of wheat and milk. If 

 milk, which contains on the average 12 pounds of nitro- 

 gen, 4| pounds of phosphoric acid and 3j pounds of 

 potash to a ton, is sold for $1.50 a hundred pounds, the 

 nitrogen is sold for $2 a pound, and the phosphoric acid 

 and potash for, approximately, 70 cents a pound. In the 

 sale of milk at this price, the rate of income to a unit of 

 exhaustion is increased nearly four times over that of the 

 wheat, though, because it is in one sense a manufactured 

 product, the cost of labor to a unit of plant-food con- 

 tained is largely increased. Again, if cream is sold, the 

 prices received for the constituents are still further in- 

 creased, while if the milk is made into butter, and that 

 alone is sold, the prices received measure the expenses 

 and profit, and the capital stock of fertility is not materially 

 reduced, though it is in another form and in another place. 



Fertility content of cereals and vegetables. 



The losses of the constituents in the sale of cereals 

 and grasses, corn, oats, wheat and hay are, too, rela- 

 tively greater than in the sale of vegetables and fruits, as 

 lettuce, celery, potatoes, tomatoes, sugar-beets, apples, 

 berries and kindred crops, though in the case of the latter, 



