May 14, 1917 
Soil Nitrogen and Nutrition of Citrus Plants 
249 
nitrogen generally showed little mottling, as did the trees receiving barn¬ 
yard manure, especially when the manure was combined with a cover 
crop. The data presented in figures 3 to 17 show that the highest 
accumulation of nitrates was found in plots A, C, G, H, and L, and also 
that the seasonal variation in nitrates is quite marked in these soils. A 
study of the degrees of mottling shows that the trees on these plots are 
more mottled than the trees on the other plots of the grove. In many 
other groves extreme mottling is frequently associated with high nitrate 
content, although some notable exceptions have been observed. 
It is well known that the percentage of nitrogen in plant tissues varies 
with the available nitrogen content of the soils, and it would seem that 
if mottle-leaf is induced by the assimilation of excessive amounts of 
nitrogen an analysis of mottled loaves, if taken at the time of mottling, 
should show a higher nitrate content than healthy leaves of the same age 
from the same tree. On October 26, 1916, a quantity of healthy and 
mottled leaves was collected from seven individual trees on plots A, 
H, O, R, S, T, and V. The leaves selected were all formed during the 
late summer and were of as nearly the same age as it was possible to 
secure. 
In order to obtain a representative sample of the two types of leaves, 
100 gm. of clean leaves were selected from each tree. The percentage 
of moisture and nitrogen found in the leaves is shown in Table XXX. 
It is observed that the moisture content of the mottled leaves is invariably 
higher than in the healthy leaves. The nitrogen content of the mottled 
leaves is also higher except from trees in plots R and T, neither of which 
has received any nitrogenous fertilizer. However, it is observed that 
the nitrogen content of the leaves from trees on plots R and T is much 
below that found in leaves taken from trees on plots which have received 
nitrogenous fertilizers. It would therefore seem that the fertilization 
has increased the nitrogen content of the leaves. However, it is also 
seen that the healthy leaves from trees on the fertilized plots are much 
higher in nitrogen than the mottled leaves from the unfertilized plots. 
Tabi*E XXX .—Moisture and nitrogen content of healthy and mottled orange leaves 
Plot. 
Moisture. 
Nitrogen. 
Healthy 
leaves. 
Mottled 
leaves. 
Healthy 
leaves. 
Mottled 
leaves. 
A. 
Per cent. 
61. 62 
60. 86 
60. 58 
62. 10 
62. 67 
60. IO 
60.86 
Per cent. 
66. 56 
66. 37 
66. 67 
63- 57 
68. 08 
63 - 7 i 
63.52 
Per cent. 
2. 69 
2. 92 
2. 91 
1-99 
2. 89 
2 . OO 
3- 06 
Per cent. 
3 - 4 i 
3 - 93 
3 * 2 5 
1. 99 
3 - 34 
2. 00 
3.40 
H... 
O.. 
R. 
S. 
T. 
V. 
