114 



FERTILIZERS. 



ing the fertility of our soils. If the value of the phosphoric 

 acid, potash, and nitrogen in the plant-food we apply is 

 less than their value in the crop we take off, then we are 

 robbing our land, and running down our farms, and vice 

 versa. Take wheat, for an illustration. The value of these 

 three elements in both stock and grain taken from the soil 

 (assuming that one-half of the nitrogen is obtained from 

 the air) is 34 cents per bushel, or $8.50 in a crop of 

 twenty-five bushels. Now, whether we are improving or 

 robbing our land turns on the fact of our having put on 

 more or less than $8.50 in fertilizers, and in the proportion 

 indicated by the analysis. 



ESTIMATES OF COST OF PLANT-FOOD IN CROPS. 



The phosphoric acid and potash are figured at the full quantities contained in the 

 crops; but the nitrogen is figured at one-half or less, assuming the balance to be fur- 

 nished by the soil and atmosphere, which is in accordance with the tendency of the 

 results of modern scientific investigation. 



In practice, on many soils half-rations of potash are ample; but, in the case of the 

 phosphoric acid, its deficiency in nearly all soils calls for full rations to be supplied from 

 outside sources. 



