May 14,1917 Soil Nitrogen and Nutrition of Citrus Plants 207 
In September, 1914, systematic studies were undertaken, in cooperation 
with the Citrus Experiment Station, to determine more accurately the distri¬ 
bution and movement of nitric nitrogen in Citrus soils and the factors con¬ 
trolling the same. Table XI shows the vertical distribution of nitric nitrogen 
in nine Citrus soils, receiving heavy applications of nitrogenous fertilizers. 
A comparison of the amount of nitric nitrogen found in the upper 6 
inches of soil in September shows that the nitrate content of the upper 
6 inches is many times that found at a depth of from 6 to 18 inches or 
18 to 30 inches. A similar distribution of nitric nitrogen is found in 
these plots during the months of October, November, December, and 
January. In February the quantity of nitric nitrogen in the upper 6 
inches was found to be very much lower than during the previous months. 
The maximum amount found at this time is in plot S and amounts to 
0.67 mgm. per 100 gm. of soil. In plot H the quantity in the upper 6 
inches has been reduced to 0.22 mgm. It is seen that, while the amount 
of nitric nitrogen in the surface 6 inches has decreased, the amount at 
a depth of 18 to 30 inches has increased in all cases. It is therefore 
obvious that the nitric nitrogen has moved downward since the sampling 
in January. During the time intervening between the samplings the 
rainfall amounted to 6.52 inches, and it would seem that this precipita¬ 
tion was sufficient to move to below a depth of 30 inches much of the 
nitric nitrogen which had accumulated at the surface during the irri¬ 
gation season. In March the nitric nitrogen content in the upper 6 
inches is much increased in plots A, G, H, L, and Q. This increase is 
apparently due to the first application of fertilizer, added on February 
14, which included sodium nitrate. Dried blood applied to plots C and 
Q or barnyard manure applied to plots F and O gives little or no increase 
in nitric nitrogen at this time. In April all plots show an increase in 
the upper 6 inches, although the gain in the manured plots is very small, 
indicating that the nitrogen in the manure becomes available very slowly. 
The plots were irrigated from April 15 to 18. Following the irrigation 
2.20 inches of rain fell. It appears from the data secured that the com¬ 
bined effect of the irrigation and rainfall between the samplings in April 
and May caused a marked downward movement of the nitric nitrogen, 
so that none of the plots showed any concentration of nitrates in the sur¬ 
face 6 inches. Even at a depth of 30 to 42 inches the nitrates were much 
lower than during the previous month, indicating a downward move¬ 
ment below feet. The second and third applications of fertilizer 
were applied on May 8 and July 2, respectively. As the season advanced 
it was observed that there was a-marked accumulation of nitrates in the 
upper 6 inches, but no increase in the lower layers. The distribution 
throughout the year indicates that the application of water in furrows 
has very little effect in carrying nitric nitrogen down, but that rainfall, 
when sufficient to penetrate the soil to considerable depth, is very effect¬ 
ive in causing a downward movement of nitrates and other soluble salts. 
