38 
COLORADO EXPERIMENT STATION 
with ammonium sulphate, while the California samples were divided 
among the three substances. The fact that these soils upon the basis 
of their ability to produce nitric nitrogen from different nitrifiable ma¬ 
terials fall into more or less well defined natural geographical groups, 
suggests rather strongly the presence of a nitrifying flora in each 
group, distinct to a greater or less degree from that of another group. 
Further evidence in support of this view is to be had in the sequence in 
which the different nitrifiable substances yielded nitric nitrogen in the 
different groups. All of the southeastern samples, that reacted pos¬ 
itively, responded in the following order: Dried blood, ammonium car¬ 
bonate, ammonium sulphate. The Texas-Oklahoma group gave this 
sequence: Ammonium carbonate, dried blood, ammonium sulphate. The 
Colorado samples constitute a third class, in which the prevailing order 
is ammonium sulphate, ammonium carbonate, dried blood. The num¬ 
ber of samples in the first two groups is too small to warrant any 
positive assertions along this line, but the results are certainly sugges¬ 
tive. 
Seven of the nine or 77.77 per cent, of the soils that made the largest 
gain in nitric nitrogen from dried blood gave second place to ammonium 
carboinate and third place to ammonium sulphate; seven out of seven or 
100 per cent, of those that produced most from ammonium carbonate 
followed next with the dried blood and then the ammonium sulphate; 
three of the five or 60 per cent, of those that gave first place to am- 
monium sulphate, followed with dried blood and then ammonium 
carbonate. 
The average amount of nitric (nitrogen produced by a positively 
reacting soil in each series was as follows : Ammonium sulphate, 152.82 
p. p. m.; ammonium carbonate, 214.76 p. p. m.; dried blood, 267.39 
p. p. m.; check 47.08 p. p. m. 
The average amount of nitric nitrogen produced by a foreign soil 
in each series, all samples taken into consideration, positive and nega¬ 
tive, was as follows: 
Ammonium sulphate, 110.36 p. p. m.; ammonium carbonate, 161.63 
p. p. m.; dried blood, 214.72 p. p. m.; check 44.93 p. p. m. 
Considering the positively reacting soils in each series or those 
which showed an increase in nitric nitrogen over the checks, we find 
that 29.41 per cent, made their largest gains from ammonium sulphate, 
41.48 per cent, from the ammonium carbonate: 50 per cent, from the 
dried blood; 29.41 per cent, made their second highest gains from am¬ 
monium sulphate; 35.29 per cent, from ammonium carbonate and 44.44 
per cent, from the dried blood. 41.18 per cent, produced their third 
largest yields from the ammonium sulphate ; 22.22 per cent, from the am¬ 
monium carbonate and 5.56 per cent, from the dried blood. The re¬ 
sults point clearly to dried blood as the most fertile source of nitrogen 
for the formation of nitrates by the majority of the foreign soils; am¬ 
monium carbonate comes second and ammonium sulphate last. 
22.73 P er cent, of the soils produced less nitric nitrogen in the 
presence of the ammonium sulphate than the controls; 22.73 P er cent, 
gave less with the ammonium carbonate than the checks, and 18.18 per 
cent, yielded less from the dried blood than the controls. 
