May i4,1917 
Soil Nitrogen and Nutrition of Citrus Plants 
243 
The basin at Whittier mulched with bean straw contains an abundance 
of nitric nitrogen, which is less evenly distributed than might be expected 
under this system of irrigation. In the first two sections there is a 
tendency for the nitrates to increase from boring 1 to boring 10. The 
uneven distribution is believed to be due to the fact that the bottom of 
the basin was about 3 inches lower under boring 1 than under boring 10. 
The low spots in the basin not only receive the greatest amount of water, 
but are covered by the heaviest mulch. The evaporation of water from 
a soil takes place most rapidly from the highest points if the capillary 
action is not interrupted. Furthermore, the mulch is thinnest on the 
high ground; therefore the concentration of nitrates would naturally 
occur at these points. However, the distribution of the nitrates is much 
better than the distribution found in the adjacent furrow-irrigated soil 
(see Table XXIV). In the basin-irrigated soil only about 7.7 per cent 
of the nitrogen in the first 4 feet is found in the upper 3 inches of soil, 
while in the adjacent furrow-irrigated soil about 24 per cent of the nitric 
nitrogen in the first 4 feet is found in the upper 3 inches. 
The basin at Arlington mulched with alfalfa hay shows a very satis¬ 
factory distribution of nitrates. In the upper 3 inches the variation is 
from 1.97 to 4.56 mgm. The second section shows a variation from 1.02 
to 3.25 mgm. In the third section the variation is from 0.67 to 3.72 
mgm. The next section shows a variation of from 1.30 to 3.74 mgm. 
The column of averages shows that the vertical distribution is quite sat¬ 
isfactory. As in the Whittier soil, the highest average is found at a 
depth of 12 to 24 inches. 
The basin at Arlington mulched with barley straw contains much less 
nitric nitrogen than the basins discussed above, and the vertical distri¬ 
bution is somewhat less satisfactory. The highest amount of nitrates 
are found in the upper 3 inches and the second highest at a depth of 36 
to 48 inches, which, for this soil, is probably below the bulk of the 
feeding roots. 
The basin at Riverside mulched with alfalfa hay is very low in nitrates, 
but the distribution is fairly uniform. 
The basin in the Highgrove section does not contain large amounts of 
nitrates; but, as* the supply is very well distributed, the amount is 
probably sufficient for the needs of the trees. 
While the studies on the distribution of nitric nitrogen in basin- 
irrigated soils are too limited to warrant any definite conclusion at this 
time, it would seem that the distribution of nitric nitrogen in basin- 
irrigated soils is far more satisfactory than in furrow-irrigated soils. 
The substitution of a mulch for cultivation also permits the feeding 
roots to come near the surface, and, thus, the nitrates and other plant 
food in the surface layer can be more completely utilized than under the 
furrow system. 
