the: nitrifying efficiency OF CERTAIN COLORADO SOILS 
25 
to .2 per cent, of the dry soil, that a very marked toxic effect is produced 
upon the nitrifying organisms; and that when a concentration of .4 
per cent, is reached, no nitrification takes place. This seems to be 
the most plausible explanation of the failure of our high chlorin soils 
to produce nitrate. The chlorin in these, when computed as NaCl, gives 
the following concentrations which fall easily beyond the limits of 
tolerance as established by Lipman; No. 80, 1.65 per cent.; No. 81, 
5.34 per cent.; No. 86, 1.05 per cent; No. 88, 1.36 per cent.; No. 92, 
1.30 per cent. While this accounts vary nicely for the lack of nitrify¬ 
ing efficiency on the part of five samples, it makes it very difficult 
to explain why No. 82 with 9,800 p. p. m. of chlorin or 1.61 per cent. 
NaCl should respond positively with a net gain of 540 p. p. nr of 
nitric .nitrogen. 
On the other hand, Professor Lipman has shown that the presence 
of .05 per cent and even .1 per cent NaCl has a stimulating effect upon 
nitrification. Almost all of our positively reacting soils contain mod¬ 
erate amounts of sodium chlorid, varying from .009 per cent, to .165 
per cent, and it is not at all improbable that the chlorin acts as an 
intensifying agent to .nitrification. 
The lack of nitrifying efficiency shown by No. 78 can hardly 
be accounted for by the presence of high chlorids, since it carries con¬ 
siderably less than several of the more efficient samples. The high 
nitrites which are present, 25 p. p. m., seem to indicate a vigorous 
denitrifying flora stimulated by the sulphate, rather than retarded 
nitrification. This follows from the fact that the control increased 
but very little, .24 p. p. m., in nitrous nitrogen and none at all in nitric 
nitrogen, while with ammonium sulphate added, there was a loss of 
nitrates and an appreciable increase of nitrites. Are we to infer from 
this that the (NH^aSO* has favored the reducing agents? The failure 
of the control to increase in nitrogen would seem to support the view 
that the nitrifying organisms were either absent or the conditions were 
very unfavorable for their development. What has been said here ap¬ 
plies equally well to No. 92, except that the high chlorin may account 
for the failure of the control to increase in nitrates. 
The conditions were somewhat different in No. 80. Here we have 
evidence in the increased nitric nitrogen of the control that the nitrify¬ 
ing organisms were moderately vigorous; however, the addition of 
the ammonium sulphate has retarded their activity to a very marked 
degree as indicated by the 68 p. p. m. of nitrite nitrogen and 23 p. p. m. 
of nitrate nitrogen as compared with .9 p. p. m. and 50 p. p. m. respect¬ 
ively in the control. 
Any interpretation that we might give to No. 86 would be little 
more than mere conjecture, other than to state that something has 
either interfered with nitrification or that denitrification has been ex¬ 
ceedingly rapid in the presence of the ammonium salt. In either case, 
we should expect to find the nitrates higher than they are. That the 
nitrifying organisms are present there is no question for the control 
shows a material gain. 
