No. «. DEPARTMENT OF AGRICULTURE. 347 



vided samples from this depth are brought under conditions favor- 

 able for nitrification. 



3. That at depths greater than 36 inches the proportion of nitrates 

 which can be found is small. 



The large quantities of nitrates produced in 285 days, calculated 

 as 335 pounds per acre, in terms of nitric nitrogen, show that our 

 soils when brought under the most favorable conditions for nitrifica- 

 tion can be made to produce nitrates at a rate far in excess of the 

 needs of the most exacting crops. 



Again, the small proportion of nitrogen converted into nitric acid 

 in a single year, as compared with the total nitrogen of the soil, as 

 shown in the last column of Table VI, demonstrates, furthermore, 

 that virgin soil will at least become abundant sources of nitrogen to 

 growing crops for scores of years. 



The question of nitrogen supply in even ordinary soils becomes, 

 therefore, a question of controlling nitrification and of conserving the 

 supplies of nitrates produced by nature. It is not to be supposed, 

 however, that anything like the supplies of nitrates obtained in the 

 preceding experiments can be realized by ordinary tillage to the 

 depths indicated. The production of an amount of nitric nitrogen 

 in any wise approaching 335 pounds to the acre is, therefore, not 

 to be expected. Were it so nature would be most w^asteful in her 

 operations, a charge which can never be truthfully brought against 

 her. 



A crop of wheat at the rate of 15 bushels of grain per acre will 

 require something like 24 pounds of nitrogen; therefore to produce 

 normal crops the economy of nature would demand that amounts of 

 nitric nitrogen comparable to the actual needs of crops should be 

 produced. This would be true to an approximate degree, provided 

 the roots had complete possession of the land, down to the lower 

 limits of nitrification, and also provided such crops had possession 

 of the land during every month of the year. 



In the case of wheat for instance, neither condition holds and con- 

 sequently the crop being unable at all times to utilize nitrates as 

 fast as they are produced, there must needs be considerable loss. 



The fact that the drainage waters from unmanured wheat fields 

 show an amount of nitric nitrogen approximately equal to that used 

 by the crop is an indication that there is produced in the soil each 

 year a stock of nitrates more than double in quantity that which the 

 crop itself can utilize. 



The relation between the quantity of nitrogen removed by a crop 

 and that present in the drainage water is brought out in the follow- 

 ing Table VII by Lawes and Gilbert. The figures show (1) the num- 

 ber of pounds of nitrogen per acre in crop and in drainage water; 



