240 
Journal of Agricultural Research 
Vol. IX, No. i 
irrigation given the middles farthest from the pipes left the nitrates in 
the upper 18 inches of soil. However, as only one set of samples was 
taken on each date the results may be due in part, or entirely, to a 
lack of uniformity in distribution. 
Table XXVI .—Distribution of nitrates in soils at Covina, Cal., irrigated by an over¬ 
head system of irrigation. Season of 1915 
[Results expressed as milligrams of nitrogen per too gm. of soil) 
Depth. 
July 14. 
Aug. 2. 
Oct. 28. 
Nov. 20. 
No mulch; 
dry middle. 
Mulch; 
dry middle. 
No mulch; 
wet middle. 
Mulch; 
dry middle. 
Mulch; 
dry middle. 
No mulch; 
wet middle. 
No mulch; 
wet middle. 
Inches. 
0- 6. 
6-18. 
18-30. 
30-42 . 
42-54. 
2. 14 
4. 41 
. 21 
. 12 
2. 94 
2. 08 
3 - 43 
*25 
I. 81 
4-03 
.28 
4.69 
3-43 
I- 33 
. 28 
2. 68 
2. 68 
2. 68 
.98 
I. OI 
.81 
30 
I. l6 
0.63 
. 70 
• 70 
.91 
.98 
I. 02 
i- 54 
54-66. 
66-78. 
During the latter part of the irrigation season the grove received 
heavier applications of water, amounting to approximately 4 inches on 
August 10, 5.4 inches on September 24, and 2.8 inches on October 20. 
A comparison of the distribution of the nitrates in the wet and the dry 
middle of the mulched soil on August 2 and October 28 shows that the 
influence of the larger application of water is clearly apparent. In the 
dry middle on August 2 the bulk of the nitric nitrogen was found in the 
upper 18 inches of soil, while it is evenly distributed in the dry middle 
on October 28 to a depth of 30 inches. Samples drawn from the 
unmulched portion of the grove on October 28 showed a nitrate content 
so much below the amount found on August 2 that it was thought advis¬ 
able to draw samples from the deeper layers; consequently, on November 
20, samples were taken to a depth of 78 inches. In these samples the 
highest nitrate content was found in the soil drawn from a depth of 66- 
to 78 inches, thus indicating that the nitrates had been carried to a 
depth of several feet by the irrigation water applied during the latter 
part of the summer. 
During the season of 1916 a large number of samples were taken from 
the same grove at Covina on August 9, August 30, and September 2. 
The soil samples were taken by driving a rectangular tube (2 by 4 by 18 
inches) into the soil to a depth of 3 inches, thus removing a block of soil 
2 by 4 by 3 inches. 
This method of sampling proved, quite satisfactory when the moisture 
content of the soil was sufficient to causp the soil to pack into the tube so 
that the exact block desired could be removed. When the soil was light 
in character and the moisture content low, it was necessary to drive the 
