No. 6. DEPARTMENT OF AGRICULTURE. 341 



fyiug ferments. In ordinary arable land, however, the quantity 

 of organic matter, or humus, never reaches a height sufficient to 

 interfere with the process of nitrification, and hence only in rare ex- 

 ceptions does this factor enter into the question of nitrification. 



Aeration and Cultivation. 



The nitrifying ferments are what are technically called aerobic, 

 that is, they grow only in the presence of atmospheric air. 



Schlosing^^ has determined the rate of nitrilication in a moist 

 soil in an atmosphere containing various proportions of oxygen as 

 follows: 



1. When oxygen was entirely absent there was a reduction of 

 nitrates and an evolution of free nitrogen. 



2. With 1.5 per cent, of oxygen nitrihcation was marked. 



3. With 6 per cent, of oxygen the quantity of nitrate produced 

 was more than double the above (2). 



4. With 16-24 per cent, of oxygen the quantity of nitrate produced 

 was more than four times that in (2). 



The effect of stirring and pulverizing the soil upon the growth of 

 cro})s has long been known, and long before the philosophy of the 

 operation itself was in any wise understood. 



Among other reasons why cultivation is beneficial is the fact that 

 it aids nitrification by bringing the oxygen of the air into more 

 immediate contact with the nitrifying ferments. The effect of stir- 

 ring and pulverizing the soil is well shown in an experiment by 

 Deheraine.^^ 



Six pots filled with soil, which had remained undisturbed for two 

 years, were selected. Three of the pots had their soil emptied on a 

 clean floor in separate piles, and each lot was kept stirred and pul- 

 verized from time to time for a period of six v>'eeks. In three of the 

 pots the soil remained untouched. At the end of the period the 

 nitrates in the several soils were determined, when it was found 

 that the average percentage of nitrates in the three stirred and pul- 

 verized soils was 23.7 times that found in the soils which had re- 

 mained undisturbed in the pots. While it is not presumed that 

 ordinary farm cultivation will produce as marked results as the pre- 

 ceding experiments indicate, it is,nevertheless, clear that the effect of 

 cultivation is to markedly increase nitrification, and in a ratio pro- 

 portionate to its thoroughness and frequency. 



In this principle we have the explanation of why the late culti- 

 vation of orchards is inadvisable. Nitrification is more active in 

 autumn than at any other time. This activity would be increased 

 enormously by cultivation, resulting in the production of large 



