234 
Journal of Agricultural Research 
Vol. IX, No. 7 
Highland soil was found to be very low. This grove bore a cover crop 
of Melilotus alba at the time the samples were taken, and it is believed that 
the low nitrate content is due to the growth of this crop. A number of 
soils on which melilotus was growing have been analyzed for nitrates from 
time to time during the growth of the crop, and it has been found that 
the growth of melilotus invariably reduces the nitrate content of the 
soil very materially. 
Table XXV. —Distribution of nitrates at right angles to furrows in soils at Redlands , 
Highland, and Rialto, Cal. 
[Results expressed as milligrams of nitrogen per ioo gm. of soil] 
Locality and date 
of sampling. 
Depth. 
Boring No. 
Aver¬ 
age. 
1 
2 
3 
4 
5 
6 
7 
8 
Redlands, soil A 
(sampled Aug. 22, 
1516) . 
Inches . 
0- 3 
3- 6 
6- 9 
9-12 
12-24 
24-36 
, 36-48 
0- 3 
3 “ 6 
6- 9 
. 9-12 
0- 3 
3- 6 
6- 9 
9-12 
. 12-15 
0- 3 
3-6 
6 - 9 
9-12 
0.18 
.18 
.ix 
O.74 
•33 
. XI 
.11 
4.94 
I.06 
.XX 
•25 
14.18 
2.18 
.46 
.IX 
4.24 
.88 
•25 
.18 
4.17 
•32 
.08 
•15 
1.09 
.18 
.18 
,05 
0.25 
.08 
.XX 
4.89 
.67 
.18 
.14 
. 11 
.18 
. 11 
4-79 
. 71 
.46 
.24 
x. 21 
•56 
. 10 
. 10 
.04 
6.15 
3 * 3 ® 
.38 
•37 
Redlands, soil B 
(sampled Aug. 22, 
1916) . 
Highland (sampled 
Aug. 1,1916). 
Rialto (sampled 
Aug. 22,1916. 
•39 
.46 
.22 
•IS 
•IS 
.IE 
.03 
.60 
.18 
. XI 
1-44 
•36 
•33 
•65 
.19 
3*30 
.XI 
.11 
.01 
3.61 
•95 
.18 
•32 
8.58 
•SO 
.88 
.18 
5 * 5 ° 
.18 
.XX 
.IX 
.ox 
9.84 
13. 20 
•67 
•74 
4.92 
3.63 
•67 
•IS 
x. 16 
.11 
•IS 
.08 
• ox 
12.92 
2.77 
•S 3 
.60 
. 9.86 
•53 
•39 
.22 
.18 
•IS 
.08 
.XI 
.08 
6.62 
S-SO 
•53 
•SO 
3*33 
•39 
•25 
•IS 
.XX 
.11 
.04 
.11 
. XX 
2.91 
2.98 
•S 3 
•32 
•57 
•IS 
.22 
.XX 
•13 
•36 
.XX 
.08 
•03 
■ X. 02 
•S 3 
• XX 
. 18 
.XI 
.04 
.08 
.ox 
•S 3 
•29 
.18 
The Rialto soil was extremely sandy at the surface, and below a depth 
of 12 inches it was so filled with coarse gravel and rock as to make sampling 
almost impossible. About 92 per cent of the nitrogen in the surface foot 
of this soil is found in the upper 6 inches, in which no feeding roots 
could be located. It would therefore seem that most of the nitric nitro¬ 
gen in this soil can be of no value until carried down within reach of the 
roots. The very gravelly nature of this soil would seem to make it readily 
subject to leaching, and it is probable that the nitrates which have 
accumulated at the surface during the irrigation season will be carried far 
beyond the reach of the roots during the rainy season. 
FORMATION OF NITER SPOTS IN CITRUS SOILS 
The accumulation of nitrates in surface spots in western soils was first 
observed by Hilgard (5), who attributed their formation to a rapid nitri¬ 
fication of the organic matter. Regarding the effect of rainfall on the 
accumulation of nitrates Hilgard wrote as follows (p. 68): 
Of course it is only in arid climates that the accumulation of nitrates can usually 
occur; for in the region of summer rains the nitrates formed during the warm season 
will inevitably be washed into the subdrainage, unless restrained by absorption by 
the roots of vegetation. 
