230 PLANT-FOOD AND AGRICULTURE. 



keep it near the surface at first, as we are quite certain it will pass 

 downward into the root pasturage, and we are never quite sure 

 against a small waste. 



Nitrogen is the expensive element of plant-food. As usually 

 supplied, it is in the form of ammonia, or a nitrate, generally 

 nitrate of soda. When sulphate of ammonia is the source of sup- 

 ply, and our crude material contains about 25 per cent, of ammo- 

 nia, each 100 pounds furnishes 21 pounds of nitrogen, which costs, 

 when the crude material is selling at 5^ cents a pound, about 26 

 cents a pound. Nitrate of soda of commerce, 95 per cent, purity, 

 furnishes about 17 per cent, of nitrogen, which, when the nitrate 

 is selling at 4 cents a pound, stands us in at about 24 cents a 

 pound. Nitrogen is also obtained from many wastes, notably from 

 dried blood. When dried blood contains 14 per cent, of ammonia, 

 it furnishes about 11| per cent, of nitrogen, and this costs about 

 24 cents a pound, the blood being purchased at 3 cents a pound. 



It makes some diflference to the crop in what form of combina- 

 tion our nitrogen occurs, because some plants feed on diflerent 

 combinations at different periods of their growth. Yet the dis- 

 cussion of this point further is outside of the scheme we have laid 

 down for this essay. 



When a nitrogen salt is added to the soil, it becomes decomposed 

 in the presence of moisture, the acid constituent passes quickly 

 through the soil, while the base, if ammonia, is retained to a cer- 

 tain extent, but not as strongly as phosphoric acid or potash. It 

 is, hence, quite readily diffused through the soil, and is quickly 

 supplied to the roots of our plants. Hence, in using a nitrogenous 

 fertilizer, we can anticipate speedy results. It is, however, on 

 this very account, subject to waste, and on account of its costly 

 nature, it is the farmer's duty, while supplying it in abundance for 

 the wants of the plant, to beware of any excess.* 



Ilaving now treated briefly these three important elements of 

 plant nutrition — phosphoric acid, potash, and nitrogen — we will 

 remark that, oftentimes, their price may be cheapened by buying 



♦To show the effect of exposure on the ammonia in manures, as previously discussed, 

 ■we give Dr. Voelckcrs's determination on fresh horse-dung as gathered from stables, 

 before being mixed with the heap. 



In bis experiment, the percentage of ammonia, which was drawn out by long-continued 

 boiling, amouuted to 0.0033. This would be .066 lbs. of ammonia a ton. As ammonia 

 can be purchased for about 20 cts. a lb., the greatest possible loss would be 1 32-100 cts. 

 a ton. The loss in practice, however, would not equal this which was obtained by means 

 of boiling water. 



