DISCUSSION" OF RESULTS OF DETERMINATIONS. 25 



itself inhibit nitrification, just as excessive dryness would check the 

 growth of any other plant. 



It seems evident, therefore, that the decrease in amounts of nitrates 

 can not be wholly explained by either moisture content of the soil, 

 denitrification, ammonification, or temperature. A shortage in or- 

 ganic food supply may have been one of the principal causes, but it 

 is also possible that the amounts of nitrates accumulated by the 

 nitrifying organisms would inhibit further increase in these salts. 

 Instances of such inhibition are not uncommon in the case of other 

 bacteria and fungi. It is also within the province of possibility that 

 the nitrifying organisms ma}^ have accumulated compounds as by- 

 products other than nitrates and that these compounds might have 

 checked any otherwise possible increase in amounts of nitrates. Even 

 when all these factors are considered there would appear to be a 

 rhythmic periodicity of nitrifying activity during the season due to 

 some unknown property of the bacteria. 



CHANGE OF WATER-SOLUBLE NITRATES TO ALBUMINOID NITROGEN. 



The disappearance of the water-soluble nitrates does not by any 

 means indicate that the nitrogen was actually lost from the soil, but 

 that it was perhaps converted into albuminoid nitrogen by other 

 groups of bacteria. It is quite conceivable that the food require- 

 ments might be sufficiently different for the two groups to permit a 

 considerable decrease in the activity of one group and at the same 

 time increase the activity of another group. It may very well be that 

 the artificial application of a food supply suitable for use by the 

 nitrifying organisms would again increase their activity to a point 

 beyond that which they formerly had reached. It is likely that had 

 water-insoluble nitrogen been determined in the same soil series, no 

 general decrease would have been found in this from June 12 to June 

 19; on the contrary, there would probably have been an increase. 

 In this connection it may be mentioned that Montanari a found least 

 amounts of "nitric nitrogen" in February, March, and June, and 

 most in July and August. He found that plats growing wheat, rape, 

 and corn 'contained more nitrates in the lower stratum (10 to 20 centi- 

 meters) than in the upper (0 to 10 centimeters); on a plat growing 

 Medicago, however, this relationship was reversed. This accumulation 

 of the (probably) albuminoid nitrogen would very possibly be of use 

 to plants the following spring and would simply be held in reserve in 

 the soil and either break down into readily water-soluble forms or in 

 other ways become available for use by higher plants. Whitson, 



o Montanari, C. Quantity of Nitric Nitrogen in Soils Variously Cultivated. Le 

 Stazioni Sperimentali Agrari Italiane, vol. 41, 1908; abstract in Experiment Station 

 Record, vol. 20, no. 8, March, 1909. 

 173 



