Oct. 9,1916 
Nitrifying Powers of Humid and Arid Soils 
67 
53 per cent of the total nitrogen of soil and dried blood under the con¬ 
ditions of the experiment. In comparison with the foreign soils as 
regards dried blood, the Riverside soils must be regarded in the same 
light as the Pasadena soils, which will be shown more fully later. 
Much the same situation as exists in the cottonseed-meal series of the 
Pasadena area soils is to be found in the Riverside area soils (see Table V, 
Group IV). There are two principal differences between them. One is 
that there are only 11 per cent of the Riverside soils, as against 21 per 
cent of the Pasadena soils, which produce less nitrate in the absolute 
from cottonseed meal plus soil nitrogen than from the latter alone. The 
other is that, on the whole, more vigorous nitrification of cottonseed- 
meal nitrogen occurs in the Riverside than in the Pasadena soils. The 
latter superiority is based mainly on the fact that more than 17 per cent 
of all the soils in the Riverside area transform more than 30 per cent of 
the total nitrogen present into nitrate, whereas the corresponding figure 
for the Pasadena area is 13 per cent. It may be added also in connec¬ 
tion with the preceding that the highest percentage transformation of 
cottonseed meal plus soil nitrogen found anywhere among the California 
soil series studied occurs in the Riverside area soil known as the 
Hanford loam, the record being 66 per cent. On the whole, therefore, 
the Riverside area soils are the most efficient of any in the nitrification 
of cottonseed meal plus soil nitrogen. This result is further strengthened 
by the fact that nearly 70 per cent of all the soils present produce 10 
mgm. or more of nitrate nitrogen in this series, as shown in Table V, 
Group IV. It is clear also that in this group there is further evidence 
of the definite relationship of degree of aridity in climate to its effect on 
the nitrifying power of soils for a given form of nitrogen. 
THE URIAH AREA SOILS 
Table VI gives the results obtained in our experiments with the 
Ukiah area soils which were carried out in a manner similar to those 
described for the other series. Of the Ukiah series, 10 soils, or over 35 
per cent of the whole number, contain more than 0.1 per cent of nitrogen. 
This is 9 per cent in excess of the corresponding figure for the Bay area, 
which ranks highest in the areas studied. Of the 10 soils just mentioned, 
6 contain more than 0.14 per cent of nitrogen, a marked contrast to the 
corresponding number for the Bay area, which is 1. Nevertheless, 
while among all the California soil series here studied the Ukiah area 
stands easily first with respect to the number of soils containing more 
than 0.1 per cent of total nitrogen, it still falls short more than 26 per 
cent of equaling the record in the same regard attained by the foreign 
soils. That, as compared with the other California series, the Ukiah 
area soils receive the place to which theoretically they should be entitled 
on the basis of total nitrogen content is also indicated in Table VI. Thus, 
