4i8 Journal of Agricultural Research voi. vn. No.» 
In the course of investigations on the origin of the so-called ‘'niter 
spots” in Colorado, Sackett (28) concluded that nitrification is unusually 
active in Colorado soils and more so than in soils from certain other 
Western States. Stewart, Greaves, and coworkers (31, 32, 33, 34) in 
Utah concluded, on the other hand, that the excessive accumulation of 
nitrates in the surface soils of certain localities is to be accounted for 
mainly by the capillary rise of nitrates from deeper strata rather than 
from unusual nitrifying activity in the soils at the present time. 
Lipman (16), by the use of the modified Remy solution method, found 
that ammonification and nitrification are most active in the first foot of 
California soils, but in some cases these processes were also found to take 
place quite actively in the subsoils down to a depth of 8 to 10 feet. He 
concluded that the deep penetration of the roots of cultivated plants may 
be accounted for in part by the active formation of available nitrogen in 
the -deep substrata. McBeth and Smith (27) also found from experiments 
with the use of actual soil as the culture medium that dried blood and 
ammonium sulphate undergo active nitrification in the first foot of 
certain Utah soils, but the activity was found to decrease markedly in the 
successive sections below the first foot until at a depth of 4 or more 
feet it almost ceased. In their experiments about 90 per cent of the 
total nitrate produced in the 5-foot sections studied was formed in the 
first foot, from which it would seem that nitrification is not particularly 
active in the substrata below the first foot. 
Greaves (8) found that, as a rule, cultivation brings about an increase 
in the numbers of organisms and in the rates of nitrification and nitrogen 
fixation in certain soils of Utah; he has also studied the effects of different 
arsenic compounds on the biological activities in soils (7, 9). Lipman 
and Burgess (17, 18, 19, 22, 23) have devoted considerable study to the 
effects of alkali salts and small amounts of copper, zinc, iron, and lead 
compounds on ammonification and nitrification in California soils. 
Recently Lipman and Burgess (24) published experiments on the rates 
of nitrification of different fertilizers in 29 different soils from California. 
Briefly, it was found that, on the whole, ammonium sulphate was most 
actively and quite vigorously nitrified in most of the soils studied. The 
rates at which the different organic substances underwent nitrification 
varied widely. In certain soils low in organic matter little or no nitrate 
was formed from dried blood or high-grade tankage, while at the same 
time cottonseed meal, bone meal, garbage tankage, and other low- 
nitrogen-containing materials were quite vigorously nitrified. They 
concluded as follows: 
In all soils of our interior arid valleys which are not very close to stream channels 
or those which for other reasons are markedly deficient in organic matter, the proper 
bacteriological and perhaps other conditions do not obtain to render into nitrates 
most economically and quickly the nitrogen of high-grade organic nitrogenous fer¬ 
tilizers. On the other hand, conditions in those same soils are much more favorable 
for the nitrification of nitrogen of the low grade nitrogenous fertilizers. Similar con- 
