Apr. 30, 1917 
Fixation of Ammonia in Soils 
149 
than 50 mgm. per 100 gm. of soil were added, the percentage fixation 
decreased as the amount added was increased. It would seem that the 
Riverside soil has the power of fixing about 900 pounds of nitrogen as 
ammonia per acre-foot, while the Lordsburg soil is capable of fixing 
more than 3,000 pounds. These figures are based upon the fixation 
which took place in 30 minutes. If the ammonia had been allowed to 
remain in contact with the soil for several days, the amount fixed would 
have been very greatly increased, as shown in Table IX. 
Table XI.— Effect of adding increasing amounts of ammonium sulphate on the fixation 
of ammonia by soils 
Nitrogen in ammonium sul- _ 
phate added per ioo gm. of 
soil. Nitrogen 
recovered. 
Mgm. 
Mgm . 
6.25. .. 
12.50., 
25.OO. 
37-5°- ■ 
50.00.. 
75.00.. 
100.00. 
150.00. 
200.00. 
300.00, 
400.00. 
2. 52 
5 * °4 
10. 36 
17. 80 
26. 60 
52. 00 
76. 44 
125- 50 
Riverside soil. 
Nitrogen 
fixed. 
Mgm. 
3- 73 
7.46 
14. 64 
19. 70 
23.40 
23.00 
23- 56 
24.50 
Nitrogen 
recovered. 
Per cent. 
40 - 3 2 
40.32 
'41. 44 
47.48 
S3- 20 
6 9-33 
76.44 
83.67 
Lordsburg soil. 
Nitrogen 
recovered. 
Mgm. 
2. 80 
5. 60 
8. 40 
11. 20 
25 * 95 
44. 80 
84. 00 
129. 60 
224. 40 
318. 00 
Nitrogen 
fixed. 
Mgm. 
9. 70 
19. 40 
29. IO 
38. 80 
49* 05 
55-20 
66. 00 
70.40 
75. 60 
82. 00 
Nitrogen 
recovered. 
Per cent. 
22. 40 
22. 40 
22. 40 
22. 40 
34* 60 
44. 80 
56. OO 
64. 80 
74 . 80 
79- SO 
EFFECT OF ALUMINIUM, IRON, POTASSIUM, SODIUM, MAGNESIUM, 
AND CALCIUM SALTS ON THE FIXATION OF AMMONIA BY SOILS 
The addition of aluminium salts to the soil 30 minutes prior to the 
addition of the ammonium salt caused a marked reduction in the am¬ 
monia-fixing power of the soil. Even the addition of 10 c. c. of N/32 
aluminium sulphate, chlorid, or nitrate reduced the ammonia-fixing 
power of the soil, as shown in Table XII. When 10 c. c. of N/i alumin¬ 
ium salts were added, about 90 per cent of the ammonia added was 
recovered. The addition of the aluminium salt 24 hours prior to the 
addition of the ammonium salts generally caused a greater reduction 
in fixation than when the aluminium salt was allowed to act but one- 
half hour. However, the time factor is of much less importance than 
the amount of salt added. The soluble iron and potassium salts, as shown 
in Tables XIII and XIV, also have a marked influence on the ammonia¬ 
fixing power of the soil tested. The potassium salts appear to have had 
somewhat less effect than the aluminium or iron salts when added in very 
small quantities; but, when added in larger quantities, these salts were 
quite as effective as the aluminium or iron salts. 
