34 
COLORADO EXPERIMENT STATION 
kansas, California(i) and Kansas, Nos. 65, 70 and 74, amounting to 
450, 526 and 640 p. p. m. respectively. I was somewhat surprised to 
find No. 65 so active, but disappointed at not getting larger returns 
from more of the California samples, since I expected them to behave 
more like the Colorado soils. The large gain in the Kansas sample ful¬ 
filled my expectations since it came from just across the state line and is 
in all respects a Colorado soil. 
The nitrites which appear in connection with No. 67, 24 p. p. m., 
suggest retarded nitrification rather than denitrification. The 700 p. 
p. in. of chlorin which the soil contained may have had something to do 
with this, although No. 74 with 2000 p. p. m. exhibits no such quantity 
of nitrites. 
The maximum net gain in nitric nitrogen from ammonium sulfate 
was made by No. 74, with 640 p. p. m. As mentioned before, this is 
essentially a Colorado soil, and it is hardly fair to the other samples to 
give it first place. The next best increase 520 p. p. m. is shown by No. 
70, California black adobe. The average gain for all of the positively 
reacting soils of this series was 150.82 p. p. m. nitric nitrogen, and the 
minimum, 1 p. p. m. by No. 71. 
Series VI. Ammonium Carbonate 
Ammonium carbonate was supplied to the soils of this series as 
the nitrifiable substance. The detailed results appear in Table 6. 
Of the twenty-two samples under study, seventeen or 77.27 per 
cent, made gains in nitric nitrogen from the carbonate of ammonium, 
while five or 22.73 per cent, failed to do so. Although the number 
of samples reacting positively and negatively is the same here as in 
the preceding set, the same soils have behaved differently. Whereas 
Nos. 58, 59 and 60 were negative with respect to the sulphate, they 
are positive in the present series. The most striking difference be¬ 
tween the results of the two series is in the increased number of soils 
that gave large net gains; with ammonium carbonate six responded 
strongly, as compared with three with the ammonium sulphate. Two of 
these Nos. 70 and 74, are the same as in Series V, but the other four 
are all different. Three of them are from California, one from Kansas, 
one from North Carolina and one from Virginia. The natural in¬ 
ference from such an increased yield of nitric nitrogen is that the a/m»- 
monium carbonate is more easily nitrified than the sulphate, so far 
as these particular soils are concerned. 
Nos. 57, 61, 62, 63, and 71 all produced less nitrate nitrogen, than 
the controls. In No. 57, there was marked inhibition of nitrification 
in the presence of the carbonate with a very little reduction. Consid¬ 
erable nitrification took place in the check. Nos. 61, 62 and 71 show 
that the same conditions existed without the denitrification. With No. 
63, the nitrifying activities were not retarded to nearly as great a 
degree, the check producing only 6 p. p. m. more nitric nitrogen than 
(1) No. 70 from California compared very favorably in nitrifying efficiency with the 
Colorado soils in all of the series. 
