Oct. 9, 1916 
Nitrifying Powers of Humid and Arid Soils 
69 
Ukiah series produce almost no nitrates, but no soil loses nitrates during 
the period of incubation. The average nitrate production is 2.84 mgm. 
in the Ukiah series and 2.09 mgm, in the Bay area series. The data for 
the percentage transformation of nitrogen into nitrates in the Ukiah 
series are also correspondingly larger than those of the Bay area, as is 
the case with the absolute data.. Thus, an 8 per cent maximum trans¬ 
formation is attained in the Ukiah series, as against one of 6 per cent in 
the Bay area series, and 5 soils besides transform more than 5 per cent 
of the nitrogen present into nitrate, as against 4 such in the Bay area. 
Table VI, Group II, helps to emphasize again the several points made 
in the foregoing discussion with respect to the behavior of sulphate of 
ammonia in the Bay area soils. Of the total number of soils in the 
Ukiah area, 8, or about 28 per cent, produce less nitrate from sulphate 
of ammonia plus soil nitrogen than from the latter alone. The corre¬ 
sponding figure for the Bay area is 20 per cent. From these facts, it 
appears that parallelism between degree of aridity of climate and the 
nitrifying power of soils for different forms of nitrogen is more firmly 
supported than ever. Thus, the Ukiah area soils as a class having more 
nitrogen and greater internal surface act more nearly like the humid soils 
than any of the other California series here studied, even though they 
are still far removed from the humid soils in that direction. Just as 
sulphate oi ammonia stimulates nitrification in the Bay area soils, so it 
it does in commensurate degree in the Ukiah area soils. As the average 
absolute nitrate production is higher from soil nitrogen alone in the 
Ukiah as against the Bay area group of soils so it is with respect to the 
sulphate-of-ammonia series of the two soil groups. The maximum trans¬ 
formation of nitrogen into nitrate is also a little higher in the sulphate- 
of-ammonia series with the Ukiah soils, it being 13 percent in the case of 
two soils, as against 11 per cent, which was the corresponding figure in 
the Bay area soils. On the other hand, there are about equal numbers 
of soils in the two areas (4 or 5) which transform more than 9 per cent 
of the total nitrogen present in this series into nitrate. The other soils 
are all considerably more feeble in nitrification. The average nitro¬ 
gen transformation on the relative basis is only slightly greater in the 
Ukiah than in the Bay area soils with sulphate of ammonia as the nitri- 
fiable material. 
Only 35 per cent of the soils in the Ukiah area produce less nitrate 
from combined soil and dried-blood nitrogen than from the former alone 
(see Table VI, Group III). This is in sharp contrast to the Bay area 
soils, for which the corresponding figure is 50 per cept, and with the 
Pasadena area, for which the corresponding value is 63 per cent. All of 
these, moreover, are in sharp contrast to the corresponding value for the 
foreign soils, which is 20 per cent. It will be noted next that very large 
nitrate productions are accomplished in the dried-blood series. Such 
quantities are in all cases much in excess of those produced by the same 
