17 
From pot experiments, where drainage was entirely prevented, the 
great superiority of ammonium nitrogen over nitrate was again dem- 
onstrated. In a series of pot experiments with the use of sterile 
quartz sand, it was found that where nitrate was the only form of 
combined nitrogen present rice made very poor growth, whereas 
ammonium forms seemed to be well suited to its needs. The net 
result of all these experiments forces the conclusion that nitrate is 
not a suitable form of nitrogen for rice, but that ammonium com- 
pounds are well adapted to its needs. 1 
In the rice-producing countries of the Orient organic manures are 
the chief source of nitrogen applied to rice soils. It has long been 
the custom of the Chinese and Japanese to grow some legume between 
crop> for the purpose of enriching the soil. Sometimes the legume 
is grown on one field, cut, and then distributed over others, so as to 
gain the benefit of green manuring with as little interruption in the 
growing of rice as possible. In addition, all sorts of organic nitroge- 
nous substances are freely applied. In Hawaii, on the other hand, 
almost no rotation is practiced. 
From a single experiment conducted by the agronomist of this 
station, however, it was found that by plowing under a few months' 
growth of alfalfa just previous to the planting of rice the yield was 
50 per cent greater than has ever been obtained on this soil by the 
application of any commercial fertilizer. In this experiment the 
alfalfa was grown on one plat, but was cut and applied to another, 
so that the effects may be attributed to the organic manure directly 
rather than to a combination of aeration and other effects, the soil 
being prepared and submerged very soon after making the applica- 
tion. Moreover, the application of different organic nitrogenous 
fertilizers at various times has always resulted in substantial in- 
creases in the yield of rice on this soil. In a series of pot experi- 
ments, for example, soy-bean cake was compared with ammonium 
sulphate. In this experiment nitrogen from each of the two sources 
was applied at the rate of 70 pounds per acre. The yield> obtained 
were as follows: 
Ammonium 
sulphate versus soy-bean cake < 
.v fertilizers foi 
rice. 
ment of plat. 
Straw. 
Paddy. 
Total. 
Grams. 
215 
107 
80 
Grams. 
13fl 
122 
01 
Grams. 
353 
Check 
141 
From the above data it will be seen that soy-bean cake brought 
about an increase of 100 per cent in the yield, but was considerably 
inferior in this respect to ammonium sulphate. The reasons for the 
1 The full data with reference to the assimilation of different forms of nitrogen by 
rice and a more complete bibliography of this subject will be found in Hawaii Sta. Bui. 24. 
