30 



SOILS OF THE TRUCKEE-CAESON IRRIGATION PROJECT. 



The fact that nitrification was feeble in tlie good soil and also in 

 one of the poor soils should not be overemphasized, for soils that will 

 nitrify under normal conditions frequently fail to do so in solutions. 

 On the other hand, the rapidity with which the nitrate bacteria 

 worked in solutions, even when they failed to do so in the soil, is 

 interesting and almost without parallel. It is not surprising that a 

 soil should fail to nitrify in solution, but it is remarkable that samples 

 which failed to nitrify when kept warm and moist — ideal conditions 

 for nitrification — should produce nitrates rapidly when inoculated 

 into solutions. 



The production of ammonia from organic material by soil bacteria 

 furnishes a means of measuring the power of the soil flora to break 

 down nitrogenous organic substances. Thus it would seem that the 

 soils of the plats in which organic matter remained indefinitely in a 



, ^1200 

 |||I00 

 ^2 1000 

 {o|900t 



1^ 



DEPTH /^Tl^MCH S/iMPlES MVFPE T/JHEN- 



.d'ToS" 



6toI2" 



/' 1 /-." 



\2n\& 



" r\»" 



I8to24' 





Fig. 19. — Diagram showing the ammoniflcation of peptone in 7 days in samples of soil from plat 350 (good 

 soil) and from plats 330 and 340 (poor soil), Truckee-Carson Experiment Farm. 



state of preservation must have a veiy low ammonifying power. 

 The medium described previously, consisting of 1.5 per cent peptone 

 and inorganic salts, was inoculated with samples from plats 330, 

 340, and 350, and the ammonia produced determined at 10-day and 

 20-day incubation periods by distillation with magnesia.^ The 

 results of this experiment are shown in figures 19 and 20. 



As the ammonification of the samples of poor soil, plats 330 and 

 340, was very similar, the results are averaged and shown as a single 

 curve. 



The fact that there is no increase between the 7-day and 15-day 

 periods indicates that the maximum had been reached before an^^ 



' Dr. J. G. Lipman has recently suggested the use of dried blood as a source of 

 nitrogen for work of this character. See Lipman, Jacob G., and Brown, Percy E., 

 "Experiments on Ammonia and Nitrate Formation in Soils," in Centralblatt fiir 

 Bakteriologie, Parasitenkunde und Infektionskrankheiten, pt. 2, vol. 26, no. 20-24, 



Ai)ril <),iyio, pp. rj<)0-(i:i2. 



