7o 
Journal of Agricultural Research 
Vol. VII, No. a 
soils in the sulphate-of-ammonia or the soil-nitrogen series. Thus, 8 
soils in a total of 28 produce more than 20 mgm. of nitrate nitrogen 
under the conditions of the experiment. Allowing for one or two excep¬ 
tional soils, the break between the high nitrate-producing soils and the 
rest in the blood series is very abrupt. As against the 8 soils just referred 
to in the Ukiah series, there are but 3 in the Bay area series of a corre¬ 
sponding class. In general, nitrification of dried-blood nitrogen proceeds 
very much better in the Ukiah series than in the Bay area soils. In 
fact, the discrepancies in nitrifying powers between the two soil groups 
are better exemplified with dried blood than with any other form of 
nitrogen. With one exception, all the soils in the dried-blood series 
which produce more than 20 mgm. of nitrates contain considerably more 
than 0.1 per cent of nitrogen, and are all possessed of large internal sur¬ 
face. The one exception mentioned is Mendocino gravelly loam, which 
contains very nearly 0.1 per cent of nitrogen and has a large interna^ 
surface besides. Owing to the higher nitrogen content in many of the 
soils of the Ukiah area than in corresponding soils of the Bay area, the 
relative figures for the two areas using dried-blood nitrogen as the nitri- 
fiable material do not differ as much as the absolute figures. Never¬ 
theless the relative values are again distinctly in favor of the Ukiah 
area soils. 
A study of Table VI, Group IV, brings us to a consideration of cotton¬ 
seed-meal nitrogen in its relations to the soils of the Ukiah area. As a 
result of such consideration we find that 40 per cent of the soils concerned 
produce less nitrate from cottonseed meal plus soil nitrogen than from 
the latter alone in every case. This is a behavior with respect to cot¬ 
tonseed-meal nitrogen very similar to that evinced by the foreign soils, 
the corresponding percentage for which was 37. The latter is obtained 
even with a few arid and semiarid or otherwise peculiar soils included, as 
previously pointed out. On the other hand, the corresponding figure for 
the Bay area soils is 26 per cent, and it is much lower for the other areas. 
In other words, it would seem that the Ukiah soils not only approach very 
closely in their behavior to cottonseed meal that of humid soils, but also 
that the curve in that respect shows a gradual decline with an increase in 
the aridity of the climate concerned. The maximum absolute produc¬ 
tion of nitrate is 29.49 nigm. as seen in Table VI, Group IV, accomplished 
by the Diablo clay. This record is surpassed in two cases in the Bay area 
series, and nearly equaled in two others. 
It may be well to summarize briefly from one or two points of view the 
results which were obtained in the experiments with the California soils. 
In a similar manner, therefore, to that employed in Table II for the 
foreign soils, Table VII gives for California the percentage of soils in 
each area which transformed more than 10 per cent of the total nitrogen 
in a given culture into nitrate, giving every form of nitrogen separately. 
