Dec, 4, 1916 
Nitrification in Semiarid Soils 
433 
The above shows that large amounts of nitrite may accumulate wh$n 
high concentration of dried blood have been used, but with a low concen¬ 
tration such is not the case. It is noteworthy that high concentration 
of other nitrogenous materials, such as bone meal, ammonium sulphate, 
and ammonium carbonate, all have been found to promote the accumu¬ 
lation of large amounts of nitrite in incubation studies. 
Alkali salts also exert marked effects upon the accumulation of nitrites 
as shown by Table IX, 
Table IX .—Effects of sodium carbonate on the accumulation of nitrite 
After two weeks. 
After four weeks. 
. Nitrogenous material added. 
Sodium 
carbonate 
added. 
Nitrite 
nitrogen. 
Nitrate 
nitrogen. 
Nitrite 
nitrogen. 
Nitrate 
nitrogen. 
None.... 
Per cent. 
P. p. m. 
P. p. m. 
P. p. m. 
P . p. m. 
None. 
O 
l6. 2 
O 
48. O 
0.1 per cent of dried blood. 
...do_ 
O 
84. O 
0 
110. 0 
Do. 
0. I 
Trace. 
86.0 
0 
100. 0 
Do.*.t. 
0.25 
* 5 -o 
19. 2 
25.O 
102 . O 
Do.. 
0.0625 per cent of ammonium sul¬ 
0. 5 
Trace. 
5 
O 
2. O 
phate . 
None. 
0 
68.0 
0 
104.0 
Do. 
0.1 
Trace. 
106. 0 
0 
l6o. O 
Do. 
0. 25 
62. 5 
10. 0 
93-8 
79.0 
Do.... 
°-5 
J * 7 
i- 7 
o-S 
I.9 
Not more than a mere trace of nitrite was found where a concentration 
of 0.1 per cent of sodium carbonate had been added, and no effect was 
produced on nitrate formation; but considerably greater amounts of 
nitrite than nitrate occurred after .two weeks’ incubation where a con¬ 
centration of 0.25 per cent of sodium carbonate had been added. How¬ 
ever, after four weeks most of the nitrite formed from dried blood had 
become oxidized to nitrate; while in the case of ammonium sulphate, 
the concentration of nitrite after four w T eeks still exceeded that of nitrate. 
The addition of 0.5 per cent of sodium carbonate entirely inhibited the 
formation of either nitrite or nitrate. 
It has been found that a concentration of from 30 to 40 mgm. of nitrogen 
in the form of sodium nitrite per 100 gm. of soil entirely inhibits the for¬ 
mation of nitrate in the soil from the experimental plots. With lower 
concentrations the nitrite was completely oxidized in four weeks’ time. 
, These results taken in connection with the preceding indicate that when 
abnormal soil conditions are brought about, the concentration of nitrite 
produced in the oxidation of nitrogenous materials may become so high 
as in itself to inhibit nitrate formation. 
CONCLUSIONS 
In the preceding investigations it has been shown that the amounts of 
nitrate formed from dried blood, bone meal, or ammonium sulphate dur¬ 
ing four weeks’ incubation varied enormously when different concentra¬ 
tions were employed. This is true in regard both to the absolute amount 
66846 °— 16 -- 2 
