32 
ble decomposition at 150° C, while at 200 and 250° C. practically 
total decomposition took place. Heating to 100° C. had but little 
effect. Steam heat at 2 atmospheres pressure brought about some- 
what less decomposition than dry heat at 150° C. 
EFFECTS OF HEAT ON THE AMMONIA CONTENT. 
In the next table will be found the data showing the effects of heat 
on the ammonia content. 
Effects of heat on the ammonia content of soils. 
[Ammonia nitrogen expressed in parts per million of air-dried soil.] 
Temperature. 
Soil 
No. 9. 
Soil 
No. 290. 
Soil 
No. 292. 
Soil 
No. 329. 
Soil 
No. 335. 
Soil 
No. 407. 
Soil 
No. 411. 
Soil 
No. 428. 
28.0 
23.8 
67.2 
187.6 
40.6 
83.3 
18.1 
19.6 
45.2 
464.8 
206.5 
51.1 
11.2 
10.5 
32.2 
174.3 
336.0 
16.8 
56.0 
64.4 
81.6 
218.4 
28.0 
77.7 
12.6 
18.2 
17.5 
32.2 
19.6 
16.1 
9.1 
13.5 
28.7 
368.2 
114.8 
46.2 
19.6 
28.0 
77.7 
170.8 
98.0 
69.2 
63 7 
oo°c 
72 8 
150°C 
127 2 
200°C 
274 4 
250 V C 
238 
Steam pressure, 2 at- 
112 7 
The ammonia content of soils Nos. 329 and 428 before heating is 
here shown to be abnormally high. Generally soils contain ammonia 
to the extent of a few parts per million only, whereas the nitrate con- 
tent may rise to considerable concentration. 1 
Under the influence of heat the ammonia content of all the soils 
studied was greatly increased, practically reaching a maximum at 
about 200° C. Above this temperature a falling off took place which 
was probably due to a loss of ammonia through volatilization. We 
here have, therefore, some interesting and, as seems probable, very 
important facts. As pointed out above, heat considerably increases 
the solubility of the inorganic matter. Here it is shown that the 
ammonia content is enormously increased also. 
Formerly little attention was given to the ammonia content of soils 
except in its relation to nitrification. During the past few years, 
however, the idea that ammonia may serve as a direct source of nitro- 
gen to higher plants has steadily gained ground. It is now known 
that certain aquatic plants, rice in particular, not only can utilize 
ammonium nitrogen but that this form of nitrogen is better adapted 
to assimilation by rice 2 than is nitrate. Other crops 3 have also 
been found to be able to transform ammonia into proteids with 
i Ammonia in soils, produced by biological agents, has for some time been looked upon as being merely 
a transitional state, its formation being essential to nitrification. The nitrifying organisms seize on the 
ammonia and convert it into nitrites and then into nitrates, thus effectively preventing an accumulation 
of ammonia in the soil at any one time. One of the essentials of vigorous nitrification, however, is free 
oxygen, while ammonirication may take the place under anaerobic conditions. In many Hawaiian soils 
aeration is very low, and for this reason (perhaps others), nitrification frequently does not keep pace with 
ammonification. 
2 See Hawaiian Sta. Bui. 24. 
s Kriiger, Landw. Jahrb., 34 (1905), No. 5, p. 761. 
