Oct. 9, 1916 
Nitrifying Powers of Humid and Arid Soils 
65 
Owing to the very low total nitrogen content of the Riverside area 
soils, the relative figures for nitrate transformation given in Table V, 
Group I, are, if wholly expected, exceedingly large in many instances. 
Thus, there are six soils, or n per cent of the whole number studied, 
which nitrify more than 20 per cent of the total nitrogen present and 24, 
or 46 per cent of all the soils, which transform more than 10 per cent of 
the total amount of nitrogen present into nitrate. On the relative basis, 
therefore, the Riverside area soils are far superior in nitrifying power to 
the Bay area soils, but not so in relation to the Pasadena soils; and 
when compared with the foreign, consisting very largely of humid soils, 
the Riverside soils are much inferior even on the relative basis. 
The results obtained with the soils of the Riverside area employing 
sulphate of ammonia are perhaps the most striking of all thus far studied. 
Thus, on the absolute basis there are but 6 soils, or a little over 
11 per cent of the whole number tested, which yielded less nitrate (see 
Table V, Group II) with the combined nitrogen of the soil and of the 
sulphate of ammonia present than from the former alone. It will be 
recalled that the corresponding figures for the foregoing series were as 
follows: Foreign soils, 87 per cent; Bay area soils, 16 per cent; and Pasa¬ 
dena area soils, 21 per cent. In other words, it would appear that the 
more distinctly arid a soil's character is the more likelihood there is of its 
being favorably affected by sulphate of ammonia, or to put it otherwise, 
to have its nitrifying flora stimulated to greater activity. It will be 
noted that the 6 soils of the Riverside area which were unfavorably 
affected as to nitrifying power by the sulphate of ammonia are all 
either sandy, coarse sandy, or gravelly soils. The actual amounts 
of nitrate produced in many of the soils of this series under the 
influence of sulphate of ammonia are very large—for example, there 
are 5 soils which produce more than 40 mgm. of nitrate nitrogen under 
the conditions of the experiment and 2 other soils which produce more 
than 20 mgm. of nitrate nitrogen. There are 18 soils in the area, or 
more than 33 per cent of the whole number studied, which produce more 
than 10 mgm. of nitrate nitrogen, and 1 soil which produced as much as 
63.92 mgm. of nitrate nitrogen. It will be remembered, however, that 
even this record is surpassed by one of the Pasadena area soils with 
sulphate of ammonia and that much larger absolute productions of nitrate 
nitrogen are accomplished with other forms of nitrogen in a number of 
instances by the foreign soils. 
Partly as a result of the high absolute quantities of nitrate produced by 
soils in the Riverside area and partly owing to the relatively small 
quantity of total nitrogen present, the percentages given in the last 
column of Table V, Group II, make a very good showing. Thus, there 
are 10 soils, or about 18 per cent of the number tested, which transform 
in every case more than 20 per cent of the total nitrogen present into 
