Oct. 9,1916 
Nitrifying Powers of Humid and Arid Soils 
63 
the Bay area soils are the intermediate group in that respect, it appears 
that cottonseed meal is better suited to arid than to humid soils. It 
may be well to note here that in the different groups of soils thus far 
studied the percentages of soils producing less nitrate from cottonseed 
meal plus soil nitrogen than from the latter alone are as follows: For¬ 
eign soils, 37 per cent; Bay area, 2 6 per cent; and Pasadena area, 21 per 
cent. The first figure is doubtless too low, because the foreign soils 
include several arid and semiarid soils which were not separated for 
purposes of this calculation. 
RIVERSIDE) AREA SOILS 
Only 3 out of 52 soils of the Riverside area contain as much as 0.1 
per cent of nitrogen, or more. That is equivalent to something over 
5 per cent of the total number of soils and is strikingly low when 
contrasted with 66 per cent of such soils for the foreign soils, 40 per 
cent for the Pasadena area, and 26 per cent for the Bay area. What is 
even more striking is that including the three soils just mentioned there 
are but 8 soils (15 per cent) in the Riverside area which contain as 
much or more than 0.05 per cent of nitrogen. Over 36 per cent, or 
more than one-third of all the soils in this area, contain less than 0.03 
per cent nitrogen. Two soils contain less than 0.01 per cent nitrogen 
and four others less than 0.015 P er cent of nitrogen. Of the four groups 
of soils thus far studied, including the Riverside area, this last is clearly 
one in which the total nitrogen content is distinctly below that of all 
other groups. From the discussion already given this subject, such a 
circumstance should not be unexpected, since the general tendency is for 
more arid climates to produce soils with a lower nitrogen content than 
that of soils in a humid climate. 
When the situation is reviewed with respect to nitrate formation from 
the soil-nitrogen supply in the Riverside areas (see Table V), some further 
interesting data become evident. In the first place it is plain that the 
absolute amounts of nitrate formed are very small and, while of a 
slightly greater magnitude than those of the Bay area, are still of about 
the same order. No soil in the whole area produces, under the conditions 
noted, as much as 10 mgm. of nitrate nitrogen, the largest amount pro¬ 
duced being 7.40 mgm., produced by the Montezuma silty clay loam. 
Moreover, there are but 13 out of 53 soils, or about 24 per cent, which 
produce as much or more than 5 mgm. of nitrate nitrogen under the same 
conditions. There are, thus, more than three-fourths of the total number 
of soils tested in the Riverside area which produce less than 5 mgm. of 
nitrate nitrogen, and most of them form from 1 to 3 mgm. only. 
Here again, as in the case of the Bay area soils and the others, it appears 
impossible to find evidence for establishing a definite relation between 
