32 
COLORADO EXPERIMENT STATION 
Foreign Soils. 
In order that we might have some first-hand data with which to 
compare the nitrifying efficiency of our niter soils, we have carried 
side by side with these, twentyi-two soils from localities outside of 
Colorado. An effort has been made throughout the investigation to 
eliminate all factors that would tend to lessen the value of the com¬ 
parative study. With the exception of the collection and shipment of 
the samples, all have been handled by the same workers so that so 
far as the personal equation and methods of technique are concerned, 
the results of both series should be fair to each other and comparable 
Ammonium chlorid has been omitted from the list of nitrifiable 
substances employed in connection with these soils since our experience 
with the salt and the Colorado samples led us to believe that it pos¬ 
sessed little value as a source of nitrogen for measuring nitrifying 
efficiency. 
Series V. Ammonium Sulphate. 
In table No. 5 will be found the results of the first set of nitrifica¬ 
tion experiments with foreign soils in which ammonium sulphate was 
employed as the nitrifiable substance. The relatively low chlorids in 
these soils stand out in striking contrast to those with which we have just 
been dealing, and with the exception of Nos. 67 and 74, the chlorin is so 
low that it can be considered as a negligible quantity. 
Seventeen or 77.27 per cent, of the soils gave positive results with 
the sulphate and five or 22.73 per cent, negative. 
Among the samples which failed to produce as much nitric nitrogen 
as the controls are two, Nos. 57 and 61, which are of particular interest 
because of their peculiar physical character; both, it will be remember¬ 
ed, are sandy loams, for the most part clean, sharp, white sand, the lat¬ 
ter considerably coarser than the former, and very deficient in organic 
matter. The writer is well acquainted with both soils and can state that 
the samples are typical of the regions from which they come. It may 
be of some interest to note in passing that the Fusarium wilt of water 
melons has been so serious on the first of these that melon growing 
has been abandoned almost entirely in recent years; the first observa¬ 
tions on the Granville tobacco wilt, caused by B . solanacearum and de¬ 
scribed by Stevens(i) and the writer in 1903, were made on the tract 
from which No. 61 came. The nitrifying organisms seemed to be pres¬ 
ent in these samples as shown by the gains in the controls, but the am¬ 
monium sulphate inhibited their action almost completely; in fact, in 
No. 57, it checked it altogether, and a little reduction took place, while 
in the other sample, there was a gain of 1 p. p. m. nitric nitrogen over 
the initial content, but still less than the control. 
Nos. 58, 59, and 60 all showed the retarding effect of the sulphate 
on nitrification. That the necessary organisms were present to trans¬ 
form the ammonium nitrogen into nitrate nitrogen is clearly evident 
for all of the controls gave very appreciable gains. 
(1) Stevens, F. L-, and Sackett, W. G. ; Granville Tobacco Wilt, Bui. 188, N. Carolina 
Exp. Sta., 1903. 
