The Fixation oe Nitrogen in Colorado Soils 5 
mixtures of sulfates, carbonates and chlorids. Under special con¬ 
ditions, such as have been previously mentioned, small quantities 
of nitrates may be present. The amount of nitric nitrogen found in 
a shale underlying a cultivated mesa on which nitre spots occurred 
abundantly and from which the seepage passed into the shale, was 
0.00399 percent, 40.0 p p m. This shale had, furthermore, been 
ground with the addition of this same seepage water and dried so 
that the amount given is, even for this condition, too high rather 
than too low. 
The question whether the “black alkali” is not brought up by 
irrigating waters added, though a popular one, is perfectly proper, 
and is entitled to serious consideration, perhaps to more serious 
consideration than I gave it in either Bulletin 155 or 178 , though 
I take cognizance of it in both of these bulletins. 
Our Colorado alkalis consist essentially of sulfates, chlorids 
and carbonates. The sulfates are represented by calcic, magnesic 
and sodic sulfates. The ratio of these salts to one another varies 
exceedingly, but they are usually all present. In some cases one or 
the other may be wanting. The chlorids found are those of cal¬ 
cium, magnesium, sodium and small amounts of the chlorid of 
potassium. The carbonates are quite subordinate. Traces of 
nitrates are sometimes present, but they may be wholly absent. 
Our study of a very alkaline soil, i. e. one which was strongly 
alkalized, will present the facts that we may expect to meet with 
under these conditions. This was a soil under cultivation for the 
purpose of studying, on the one hand, the effects of the alkalis on 
the crop, and on the other, the effect of cropping and cultivation 
upon this alkalized soil. 
The alkali appeared on the surface of this soil as an incrusta¬ 
tion, attaining, under favorable conditions, a thickness of one-half 
inch or more. These incrustations carried from two to five percent 
of chlorin and from none to a heavy trace of nitric nitrogen. The 
top two inches of portions of this plot yielded as much as three and 
nine-tenths percent of water-soluble material, of which five and 
one-half percent was chlorin. The second two inches of this soil 
yielded two and one-half percent of water-soluble of which only 
nine-tenths of one percent was chlorin. The nitric nitrogen was 
determined in these samples and we find the following results 
for these and other sections of the plot. The results are given in 
parts per million of the air-dried soil, in which there may have 
been a slight increase in the nitric nitrogen during drying. 
This table shows what we found in four different sections of 
this plot on the date that the samples were taken. At the time these 
samples were taken I considered 36 p. p. m. nitric nitrogen in the 
