AMOUNT OF NITROGEN IN DIFFERENT CROPS. 191 



form of starch, gum, and of sugar, that is, of substances desti- 

 tute of mineral ingredients. 



Every moment of time is of value in the practice of farming ; 

 and, in this respect, humus is of especial importance in kitchen 

 gardening. 



Our corn plants and edible roots find in our fields, in the form 

 of the remains of a past vegetation, sufficient vegetable matter to 

 correspond to the mineral food existing in the soil, and, therefore, 

 with sufficient carbonic acid to produce a quick growth during 

 spring. Any further supply of carbonic acid would be wholly 

 useless, unless it were accompanied by a corresponding increase 

 of the mineral constituents adapted to form parts of the plant. 

 Upon a Hessian acre of good meadow land we obtain 2500 lbs. of 

 hay, according to the opinion of experienced farmers. Meadows 

 yield this crop, without any supply of organic matters, t with- 

 out any manures containing nitroger or carbon. By proper irri- 

 gation, and by treatment with ashes and gypsum, the crop can 

 be increased to double the amount. Let us assume, however, 

 that the 2500 lbs. of hay form the maximum crop ; still, it is 

 certain that all the carbon and nitrogen of the plants constituting 

 it must have been obtained from the air. 



According to Boussingault, hay, dried at the temperature of 

 boiling water, contains 45*8 per cent, of carbon (a result agree- 

 ing with analyses made in this laboratory), and 1*5 per cent, of 

 nitrogen; hay dried in air still retains 14 percent, of water, 

 which escapes at the heat of boiling water. 



2500 lbs. of hay, dried in air, correspond to 2150 lbs. of hay 

 dried at the temperature of boiling water. With the 984 lbs. of 

 carbon contained in the crop of 2150 lbs. of hay, we have also 

 removed from the acre of meadow-land 32*2 lbs. of nitrogen. 

 If we assume that this nitrogen has entered the plant in the form 

 of ammonia, it is obvious that for every 3640 lbs. of carbonic 

 acid (calculated at 27 per cent, of carbon) the air contains 39-1 

 lbs. ammonia (taken at 82 per cent, of nitrogen) ; or that, for 

 every 1000 lbs. of carbonic acid, the air contains 1 0-j T - lbs., am- 

 monia — a quantity corresponding to about -r6"aoTb" °f tne weight 

 of the air, or of -"-foVo'o °f - ts volume. 



Thus fcr every 100 parts of carbonic acid absorbed by tho 



