May 14, 1917 
Soil Nitrogen and Nutrition of Citrus Plants 
197 
slower than when vetch or melilotus was added. The highest percentage 
of nitrogen as nitrates recovered from soybeans was 30.97. The increase 
in total nitrogen is also comparatively low. 
The addition of 2 per cent of corn gave very little or no increase in the 
ammonia content, and the increase in nitrates after the first 14 days was 
very small, and in some instances no increase was found. However, 
during the latter part of the incubation period the formation of nitrates 
took place more rapidly, and at the conclusion of the experiment 62.36 
per cent of the nitrogen added in corn was recovered as nitrates in soil F, 
the average for the five soils being well above 50 per cent. The percentage 
increase in nitrogen varies from 123.3 in the virgin soil to 151.9 in soil H. 
The addition of cowpeas, like the addition of soybeans and corn, caused 
very little or no increase in ammonia. Nitrification appears to have 
started somewhat slowly; but, when once started, the increase continued 
rather rapidly until the end of the experiment. In all of the soils the 
percentage of nitrogen recovered from soybeans as nitrates varies from 
24 in the virgin soil to 50.4 in soil F. All of the soils show an increase in 
total nitrogen, although the increase is much smaller than that received 
from the addition of com. 
Black-eyed peas caused a moderate increase in ammonia in all of the 
soils. At the conclusion of the experiment the percentage of nitrogen 
recovered from black-eyed peas as ammonia varied from 1.33 in soil H 
to 7*55 * n the virgin soil. There appears to have been a slight loss in 
nitrates at the end of 14 days in all of the.soils except soil B, in which the 
increase amounted to only 0.14 mgm. During the latter part of the 
incubation period considerable quantities of nitrates were formed from 
black-eyed peas, and at the conclusion of the experiment the percentage 
of the nitrogen recovered as nitrates varied from 30.38 per cent in the 
virgin soil to 46.79 per cent in soil F. There was an increase in the total 
nitrogen in all of the soil, which varied from 18.87 per cent in soil B to 
79.95 per cent in soil F. 
The addition of 2 per cent of oats caused very little or no increase in 
the ammonia content of the soils; neither was there any increase in 
nitrates; but, on the other hand, the addition of oats seems to have 
reduced somewhat the nitrate content of all of the soils. There were small 
gains in total nitrogen in soils U and F, but small losses in H, B, and the 
virgin soils. 
In the control samples the ammonia remained fairly constant through¬ 
out the experiment, but there was a slow and quite uniform increase in 
nitrates. 
A fourth series of samples was taken from the experimental plots at 
Riverside on November 4, 1914, and handled similarly to those taken 
on August 28, except that the green manures added were generally dif¬ 
ferent. The results secured in this experiment are given in Tables VIII 
and IX. 
