THE) NITRIFYING EFFICIENCY OF CERTAIN COLORADO SOILS 37 
Of the twenty-two soils under examination, eighteen or 81.82 per 
cent, gave gains in nitric nitrogen from the dried blood; four or 18.18 
per cent, produced less than the controls. 
The eight samples which made the largest gains were Nos. 52, 55, 
60, 64, 69, 70, 73, and 74; four came from California, one from Kansas, 
one from North Carolina, one from Virginia, and one from Ohio; 
five of these are the same that gave the high yields in the preceding 
series, while Nos. 52 and 64 are new ones to the list. v 
Soil No. 60 presents a very interesting case in its behavior toward 
the different forms of ammoniacal and proteid nitrogen. With the sul¬ 
phate it gave less nitric nitrogen than the control; when associated * 
with the carbonate, a gain of 290 p. p. m. over the check resulted; and 
from the dried blood, it produced 490 p. p. m., a very nice illustration 
of the relative availability of the different nitrogenous compounds for 
the nitrifying flora of a given soil. Essentially the same relations are 
brought out in No. 55. 
Nos. 57, 61, 63 and 71 all produced less nitrate nitrogen than 
their controls; these behaved similarly in the preceding series. Nos. 
57 and 61 show evidence of some reduction. With Nos. 63 and 71, the 
negative results appear to be due to retarded nitrification rather than 
denitrification since some gain has been made over the initial nitrogen 
of the control but not as much as in the control at the end of the experi¬ 
mental period. 
Nos. 67 and 68 gave high nitrites here as in the preceding series 
and what was said there in this connection will apply equally to the 
present results. 
The maximum gain in nitric nitrogen from the dried blood was 
made by No. 55 with 650 p. p. m.; the average for the positively react¬ 
ing soils was 267.39 P- P- m - and the minimum gain 6 p. p. m. by No. 53. 
SUMMARY OF FOREIGN SOILS 
Seventeen or 77.27 per cent, of the soils under study were able to 
convert the nitrogen of ammonium sulphate into nitrate nitrogen; the 
same per cent, accomplished this transformation with ammonium car¬ 
bonate and eighteen or 81.82 per cent, with dried blood. 
The largest total amount of nitric nitrogen was produced from the 
dried blood ; the next largest from the ammonium carbonate, and least 
from the ammonium sulphate. 
The largest amount of nitric nitrogen produced by any one soil 
from ammonium sulphate was 640 p. p. m. by No. 74, a sandy loam 
from Kansas ; from ammonium carbonate, it was 606 p. p. m. by No. 
70, California black adobe; from dried blood, it was 650 p. p. m. by No. 
55, a heavy clay from Virginia. It is a significant point that the high¬ 
est yields from both of the salts were obtained by western soils, while 
the best return from the dried blood was secured by a southeastern 
sample. Without exception all of the soils from the southeastern part 
of the United States made their largest gains from the dried blood; 
those from Washington, Oklahoma and Texas gave the best results 
with ammonium carbonate; Arkansas and Kansas (also Colorado) 
