248 
Journal of Agricultural Research 
Vol. IX, No. 7 
Samples taken from plot A on October 7 show that the distribution of 
the nitrates has been materially changed by the 1.80 inches of rain. 
After the rain the largest amount of nitric nitrogen, as shown in Table 
XXIX, is found at a depth of 6 to 9 inches and the next largest at a 
depth of 3 to 6 inches. 
The distribution of nitric nitrogen in soils C and H on October 7 also 
shows that the 1.8 inches between September 30 and October 7 caused a 
movement of the nitrates out of the upper 3 inches of soil into the second 
and third sections. 
Samples taken from a clay soil at Arlington after the rain show the 
highest nitrate content at a depth of 3 to 6 inches, while the surface 3 
inches contains but little more than the soil from 6 to 9 inches. 
The rain between September 30 and October 7 fell on the soils just as 
they were being prepared for irrigation, and consequently the moisture 
content was low. In taking the samples for analysis 4 t was observed 
that the rain had been absorbed by the upper 9 inches of soil. In 
studying the columns of averages in Table XXIX it is seen that the 
movement of nitrates was also within the upper 9 inches of soil, the 
nitrates being leached out of the upper 3 inches and deposited at a depth 
of 3 to 9 inches. 
RELATION OF NITROGEN TO MOTTLE-LEAF 
Mottle-leaf, as applied to Citrus plants, is frequently accompanied by 
marked reduction in quantity and quality of fruit, and in advanced stages 
the vigor of the tree is also much impaired. As the mottling of Citrus 
plants had become quite widely distributed the cause of mottling has 
received much attention from a number of investigators during recent 
years. Many causal agents have been suggested, but none of the theories 
advanced seems to offer an entirely satisfactory explanation of this disease. 
The relation of available nitrogen to mottle-leaf has been discussed by 
Kellerman and Wright (6) and also by Lipman (7). The total nitrogen 
in a large number of Citrus groves showing various degrees of mottling 
has been reported upon by Briggs, Jensen, and McLane (1). 
In the work reported in this paper much attention has been given to 
the formation and distribution of ammonia and nitrates, and their possi¬ 
ble relation to mottling has been kept in mind. In the early part of the 
work it was shown that the ammonia content of the soils studied was 
apparently changed very little by the difference in soil treatment. The 
application of large quantities of nitrogenous fertilizers caused only a 
small increase in the ammonia, and the writer has not been able to secure 
any evidence that any relationship exists between the ammonia content 
of the soil and the character of the trees or fruit produced. 
However, during the progress of the work it was observed that those 
plots which received larger applications of nitrogen in commercial fer¬ 
tilizers generally bore badly mottled trees. The trees which received no 
