Oct. 9, 1916 
Nitrifying Powers of Humid and Arid Soils 
73 
It seems clear from Table IX that sulphate of ammonia induces under 
laboratory conditions a larger yield of nitrate in the large majority of the 
soils of arid regions than could be produced by those soils with their own 
nitrogen. The range in the percentage of such soils is not large and 
varies between 89 per cent in the Riverside area and 72 per cent in the 
Ukiah area. On the other hand, it is clear also that in the large majority 
of soils in the foreign group ammonium sulphate has the opposite effect— 
that is, to depress the nitrifying power of a soil for its own nitrogen. 
The effects of sulphate of ammonia are thus almost exactly reversed in a 
comparison of the Riverside and the foreign soils, for example. In the 
comparison made by Sackett (10) of the nitrifying power of certain 
Colorado soils (using ammonium sulphate) with certain others from 
several other States, it will be noted that the foreign soils, with the excep¬ 
tion of the California soils, acted as a class like those studied by the 
writers. Likewise, the Colorado soils are more like the arid soils which 
were described previously. Inotherwords, the Colorado soils were superior 
in nitrifying power for sulphate-of-ammonia nitrogen to soils from other 
States, even not excepting the California soils. It must be remembered, 
however, that anything more than a general analogy or comparison 
between the writers 1 results and Sackett’s is not permissible for the fol¬ 
lowing reasons: Sackett used 100 mgm. of ammonium-sulphate nitrogen, 
while the writers used 40 mgm. in the soil cultures. He inoculated the 
cultures with a fresh soil suspension in the case of every soil studied, 
which was equivalent to 5 gm. of soil, while the writers merely employed 
the soil flora existing in the air-dried soil. Sackett used a six weeks’ 
period of incubation, whereas the writers employed only a four weeks’ 
period. In several other minor respects the conditions of Sackett’s ex¬ 
periments were different, among which may be particularly mentioned 
the method of analysis employed for nitrate determinations. 
In the case of dried blood, conditions seem to be almost the reverse of 
those with ammonium sulphate. The soils of the foreign group which 
produce less nitrate from dried blood than from their own nitrogen alone 
are decidedly in the minority, but the reverse is true of the arid soils of 
California as they become more and more humid in character. Dried 
blood therefore induces a loss in nitrate-producing power in from 35 to 
63 per cent of the soils of the arid region. On the other hand, the same 
substance affects only 20 per cent of the total number of foreign soils in 
that manner. Hence, there is a stimulation to nitrification in some soils 
of the arid region induced by the presence of dried blood in them. The 
opposite is true with humid soils. 
With respect to the stimulating or retarding action on the nitrifying 
powers of the soils studied, cottonseed meal acts almost exactly like 
ammonium sulphate in the Pasadena and Riverside areas. The differ¬ 
ence between the two materials is, however, much greater in the other two 
arid-soil groups; but still in both cases the percentage of soils in which 
apparent losses in nitrifying power are induced is below that of the foreign 
