May 14,1917 
Soil Nitrogen and Nutrition of Citrus Plants 
189 
nitrogen recovered as nitrates in soil E was only 1.95, but in soil D the 
percentage recovered as nitrates amounted to 16.74. Both of the soils 
to which oats were added show gains in total nitrogen, amounting to 
95.27 per cent of the nitrogen added in soil E and 72.78 per cent in soil D. 
The addition of 1 per cent of green barley caused only slight increases 
in ammonia, and the increase in nitrates after 6 weeks’ incubation varied 
from 1.38 mgm. in soil E to 3.83 mgm. in soil D. 
One per cent of melilotus caused a decided gain in ammonia in all 
soils during the early part of the incubation period, and in soil E the 
increase in ammonia caused by the decay of the melilotus is apparent 
throughout the experiment, but after 21 days soils D and C contained no 
more ammonia than the controls. 
The increase in nitric nitrogen resulting from the addition of green 
melilotus begins during the first few days. After seven days’ incubation 
the average gain for the three soils is more than the average gain from 
oats or barley during the entire six weeks’ incubation. In soil E the 
maximum increase in nitrates is obtained after 28 days. In soils D and 
C the gain continues throughout the six weeks; but the total increase is 
less than in the soil in which the maximum gain is attained in a shorter 
period. 
None of the nitrogen added in melilotus in soils C and D remained in 
the soil as ammonia, but 6.6 per cent remained in soil E. Nearly 40 per 
cent of the nitrogen added in melilotus was recovered as nitrates and the 
nitrogen gains in.the three soils varied from 48.11 per cent of the nitrogen 
added in soil C to 66.51 per cent in soil D. 
The addition of 1 per cent of alfilaria showed an increase in ammonia 
after seven days, but after the seven-day period the increase over the 
controls was very small. Small gains in nitrates were secured in seven 
days, and the increase proceeded gradually during the six weeks’ incu¬ 
bation. 
A little less than 2 per cent of the nitrogen added in alfilaria was 
recovered as ammonia, and from 10.74 to 18.35 P er cent as nitrates. 
The nitrogen gain from alfilaria is smaller than from oats, barley, or 
melilotus. 
The addition of barley hay showed no increase in ammonia at any 
time during the experiment. Neither was there any increase in nitrates 
in this soil over the supply in the control, thus indicating that the nitri¬ 
fication of mature barley is much slower than the nitrification of green 
manures. 
Horse manure was used only in soil C, in which it caused no apparent 
increase in ammonia over the control. Nitrification proceeded slowly 
and somewhat irregularly. The gain in nitrates over the control 
amounts to only 1.29 mgm. in six weeks. Only 9.49 per cent of the nitro¬ 
gen added in horse manure was recovered as nitrates. However, there 
was a gain in nitrogen amounting to 54.41 per cent of the nitrogen added. 
