Oct. 9, 1916 
Nitrifying Powers of Humid and Arid Soils 
53 
but has, on the contrary, caused a reduction in the soil's power to render 
nitrogen into nitrate. This holds, of course, only in general, and several 
exceptions may be found to the rule. If the absolute amounts of nitrate 
produced as given in Group II of Table I are compared specifically with 
those given in Group I, it will be found that all the soils tested except six— 
namely, those from Indiana, Oregon, Texas, Utah, Wyoming, and Guam— 
produced far less nitrate when sulphate of ammonia was added to them 
than they did from their own nitrogen alone. It will be noted that of the six 
soils which did produce more nitrate under the conditions noted than from 
their own nitrogen only one is a soil belonging strictly to the humid 
region. The effects of sulphate of ammonia on the nitrification of soil 
nitrogen in humid soils is very striking and difficult to explain. The 
acidity of soils appears to be inadequate to explain the situation. 
As is to be expected, smaller absolute transformations of nitrogen into 
nitrate in soil and ammonium sulphate than in soil nitrogen mean a 
smaller percentage transformation of the total nitrogen present. Hence, 
whereas in the case of the soil nitrogen alone, 11 soils out of 47, 
or 23 per cent, transformed more than 20 per cent of nitrogen in 
every case into nitrate, only one soil belongs in that class when the 
series containing soil nitrogen plus sulphate of ammonia nitrogen is 
considered. Also, whereas nearly 66 per cent of the soils in the soil- 
nitrogen group transform in every case more than 10 per cent of the total 
nitrogen into nitrate, only about 23 per cent of the same soils in the 
ammonium-sulphate group fall in that category. These limited statis¬ 
tical illustrations on the differences obtaining between the experimental 
series resulting in the soil-nitrogen group and the ammonium-sulphate 
group are sufficiently emphatic to need no further comment at this point. 
Group I of Table I is compared with Group III, which sets forth the 
results of the dried-blood series with the foreign soils, only 10 soils out of 
47 or 48, or about 20 per cent, will be found which produced less nitrate 
when blood (1 per cent) was added to them than when only their own 
nitrogen supply was allowed to nitrify. Again, attention is called to 
what is probably a purely coincidental but interesting circumstance like 
the one above mentioned. Just as 9 of the soils which transformed more 
than 20 per cent and less than 39 per cent of their own nitrogen 
into nitrate included 7 which came from States of the Southern 
or South Atlantic group, so in this case of the 10 soils which produced less 
nitrate from dried-blood nitrogen plus the soil nitrogen than from the 
latter alone, 7 belong to the group of States which are in nearly all cases 
the same. Of the three other soils, two are from the semiarid region— 
namely, Nebraska and New Mexico—and only one is from the northern 
portion of the humid region—namely, Illinois. It is worthy of note that 
in all but the Florida and Illinois soil, of the group of 10 just considered, 
the nitrogen content is below 0.08 per cent, and in most of them is below 
0.05 per cent. 
