Fixation ot Nitrogen in Colorado Soils 
33 
tion of such water from the surface of these areas.” These 
statements referred to small areas, nitre-spots, and the ques- 
tion of immediate association of the nitrates in the soil and the 
' o^round- waters was incidental to the object had in view. Our 
present investigation is on a much broader scale and concerns 
itself directly with this relation. 
For further study of this point we sampled the surface soil 
i of 18 square miles, or sections of land. We sampled 12 of the 16, 
forty -acre divisions in each section. We united 15 subsamples 
’ in each sample. It sometimes happened that a forty was very 
difficult of access or its location was such that a sample from 
; it would have no object except to simply add one more sample 
i to the statement of results which we tried to avoid. 
I 
In this work on the soil nitrates we have at all times felt the 
need of an acknowledged upper limit above which all amounts 
! of nitric nitrogen may be considered excessive. So far as I can 
^ learn, under ordinary humid conditions, 8.0 p.p.m. is a liberal 
superior limit. I know of no effort to ascertain this limit for 
I semi-arid conditions, though the amount present in such soils 
may be both higher and more irregular than under humid con- 
ditions; still according to our observations, made on very pro- 
ductive land, 8.0 p.p.m. is a fair superior limit to assume. Our 
good, cultivated soil ranges from 5 to 8.0 p.p.m. unless under 
crop or immediately after harvest when the nitric nitrogen is 
materially below these figures, 1 p.p.m. or even less., 
The season of 1919 was an unusually dry one with us. Irri- 
gating water was so short that some of the fields planted to 
beets remained fallow till late in August or even September 
* when there was moisture enough to germinate the beet seed. It 
was unfortunate that this season, when we took our soil sam- 
ples, was so abnormal in this respect.. There was no washing 
out of the surface soil during the season, and in taking our sam- 
' pies we pushed our soil tube down into moist soil if possible. 
What the effects of such a lack of moisture may have been upon 
the biological activities going on in the soil, I do not know but I 
hoped to offset this doubt^ at least in part, by taking the sam- 
ple deep enough to obtain moist soil whenever feasible. 
In taking our samples, we began at the northwest corner 
, of the section and numbered our samples as in the accompany- 
ing diagram, which also gives the sections sampled and their 
rela tive nositiona. 
