74 
Journal of Agricultural Research 
Vol. VII, No. a 
group. The latter is none the less almost half the magnitude of the 
corresponding figure for sulphate of ammonia with the foreign soils. 
From all the foregoing considerations it appears evident that different 
forms of nitrogen exercise widely different effects on different groups of 
soils. Thus, for example, ammonium sulphate seems to enhance the 
nitrifying powers of arid soils and to depress those of humid soils. Dried 
blood seems, in general, to operate in a reverse manner, while cottonseed 
meal seems to act more like the ammonium sulphate. It will be remem¬ 
bered that conclusions similar to those reached for arid soils were drawn 
by Lipman and Burgess (7) with respect to another group of arid soils with 
which they worked. Moreover, Sackett, in the experiments cited, noted 
that the relationship of the Colorado soils to sulphate of ammonia and 
to dried blood was the reverse of the relation of the other soils which he 
studied to those substances. The position of the Colorado soil was 
similar to that occupied by the California soils with respect to the foreign 
soils. The apparently mystifying feature of the comparison lies, how¬ 
ever, in the fact that the California soils tested were in Sackett's foreign 
group (10) and, therefore, in his hands gave different results from those 
obtained by us. This may perhaps be accounted for by the fact that 
the foreign soils are considered as a whole and are not separated from 
the California soils, which in reality give much better results than, for 
example, the eastern soils with sulphate of ammonia. 
Table X has been arranged to bring together some of the figures above 
discussed with respect to the relative powers of soils to nitrify different 
forms of nitrogen. The first group shows the percentage of soils in each 
of the areas studied which transformed more than 10 per cent of the 
total nitrogen present into nitrate in the case of every form of nitrogen 
employed. The second group shows the percentage of soils in every 
area which produced a quantity of nitrate equivalent to 15 mgm. in the 
case of the foreign soils. The equivalent amount for soils other than 
those of the foreign group was determined by using the same ratio of* 
nitrate to total nitrogen which is employed in the last-named groups of 
soils, the average total nitrogen content of all soils in a given area being 
used as a basis. 
Table X .—Transformation of nitrogen in various soil areas 
Form of nitrogen. 
Percentage of soils which 
, transformed 10 per cent 
or more of nitrogen into 
nitrate. 
Percentage of soils produc¬ 
ing 15 mgm. of nitrate ni¬ 
trogen in the foreign area 
and an equivalent quan¬ 
tity based on nitrogen 
present in other areas. 
Soil nitrogen only. 
Soil nitrogen and ammonium sulphate. 
Soil nitrogen and dried blood. 
Soil nitrogen and cottonseed meal.... 
47 
47 
30 
70 
34 
47 
28 
60 
o 
6 
10 
20 
o 
xo 
14 
10 
68 
23 
47 
45 
24 
7i 
41 
75 
18 
0 
0 
71 
16 
25 
42 
30 
31 
80 
23 
21 
52 
25 
81 
63 
