May 14,1917 
Soil Nitrogen and Nutrition of Citrus Plants 
245 
there was an increase from 0.23 to 1.37 mgm., indicating that a portion 
of the nitrates removed from the surface 6 inches was deposited at a 
depth of 18 to 30 inches. In the soils which .have received barnyard 
manure the nitrates in the upper 6 inches of soil amounted to 1.65 mgm. 
on January 23, and on February 7 only 0.25 mgm. was found. During 
the same period there was an increase in nitrates at a depth of 18 to 
30 inches from 0.30 to 0.85 mgm., thus confirming thp results secured 
in the soils receiving commercial fertilizers. 
There is a marked increase in nitrates in the upper 6 inches of the 
soils receiving commercial fertilizers from February 7 to April 6. This 
increase is due to the application of nitrogenous fertilizers from February 
27 to March 1. The rainfall from February 27 to April 6 amounted to 
only 0.56 inch; and, as this quantity fell in light showers, the rainfall 
during this period could have had little or no influence on the distribu¬ 
tion of the nitrates. It is interesting to note that, while there is a 
marked increase in nftrates in the upper 6 inches of soil of the plots 
receiving commercial fertilizers, there is little or no increase from 6 to 
18 or from 18 to 30 inches in these soils. Very little increase is seen 
in the soils receiving barnyard manure, even in the upper 6 inches. As 
the manure was applied in February, it would seem that the nitrogen in 
manure becomes available very slowly in these soils. 
From April 15 to 18 about 3 acre-inches of irrigation water were 
applied, and from April 20 to May 2 the rainfall amounted to 2.24 inches. 
The soil was well moistened by the irrigation; and, as the weather con¬ 
ditions during this period were such as to permit only slight loss from 
evaporation, the rainfall during this period was very effective in moving 
the nitric nitrogen out of the surface layers. On April 6 the average 
nitrate content of the upper 6 inches of the seven plots receiving com¬ 
mercial fertilizers amounted to 2.07 mgm. On May 8 the amount found 
was only 0.42 mgm., and there was also some reduction in the lower 
layers, indicating that the nitrates moved from the surface were carried 
downward to a considerable distance. 
The nitrates in the manured soils were low during the spring, and 
the rainfall from April 20 to May 2 seems to have had little effect on 
the nitrates in these soils. However, it is quite possible that nitrifica¬ 
tion of the manures from April 6 to May 8 was sufficient to maintain the 
low nitrate content in these soils against the leaching effect of the rains. 
It is observed that a very marked increase in nitrates has taken place 
from May 8 to June 15 in the upper 6 inches of soil in the plots receiving 
commercial fertilizers, but that the increase below the 6-inch layer is 
very slight and in some cases no increase is observed. The marked 
increase in the upper 6 inches of soil at this period is no doubt due to 
the second application of fertilizer which was added May 15. 
There is also an increase in nitrates in the upper 6 inches of the ma¬ 
nured soils, which indicates that the nitrification of the manure was now 
