19 
It is here seen that ammonification proceeded at a slow rate only, 
if at all. until a certain moisture content was veaefaed (about 10 per 
cent in the case of soil 292 and 15 per cent with that of 461 >, above 
which vigorous ammonification took place, which steadily increased 
up to an approximate two-thirds saturation, then decreased as com- 
plete saturation was approached. There was. however, active am- 
monification in the completely saturated soils. This seem- to prove 
that ammonia is formed in submerged soils and that organic nitroge- 
nous fertilizers will give rise to nitrogen available to rice under con- 
ditions that prevail in rice cultures. 
As is well known, the formation of ammonia results from the 
activity of a wide range of soil organisms, bacteria and fungi, some 
of which are aerobic and some anaerobic. While the above data 
show that ammonification is more active with moisture supplies 
below the saturation point, being greatest at approximately two- 
thirds saturation ; nevertheless, the fact that ammonification can take 
place in saturated soils is of very great importance in the growth of 
rice. It makes possible the production of available nitrogen in rice 
soils without the necessity of employing cultural methods that are 
primarily designed to bring about aerated conditions. 
Free oxygen being essential to nitrification, it seems justifiable to 
conclude that nitrification does not take place to any considerable 
extent in a submerged soil. In order to throw positive light on the 
question, however, search was made for nitrates in various submerged 
soils about Honolulu, but in no instance was more than a few parts 
per million found. In some laboratory experiments it was further 
found that practically no nitrification took place in submerged soils. 
The process of denitrification, however, is of considerable impor- 
tance in this connection. As is well known, free nitrogen gas may 
be one of the products of the decay of organic manures. Likewise, 
it is also known that certain denitrifying bacteria break down nitrates 
into nitrites, ammonia, and finally into free nitrogen gas. The con- 
ditions under which the denitrifying bacteria function are extremely 
varied, but the two conditions most favorable for their activity are a 
source of food supply and a lack of free oxygen. In the rice soils of 
Hawaii these conditions are abundantly met; tfre high content of 
organic matter guarantees a source of food, while supersaturation 
excludes the air. 
A- indicated above, the denitrification processes may be conven- 
iently divided into two classes, (1) those causing a liberation of 
nitrogen from organic materials, and (2) those bringing about a 
reduction in the nitrates present. The latter of these has been the 
subject of considerable study at the Hawaii station. 
