The Fixation of Nitrogen in Coeorado Soils 43 
percent was sodic nitrate, 12.0 percent was sodic chlorid and the other 
salts were sulfates. Another exceedingly rich sample yielded 13.4 per¬ 
cent of water-soluble, of which 41.86 percent was nitrates, 10.0 percent 
chlorids and the rest sulfates. The occurrence of very small amounts of 
sodic carbonate in the aqueous extracts of soils from these spots is 
noticeable, in fact the carbonates are more frequently absent than pres¬ 
ent. Calcic carbonate, however, is always present, and usually abundantly 
so, in these soils. It should also be stated that our common alkalis 
seldom contain large amounts of carbonates. There does not appear to 
be any relation between the amount of nitrates and that of any other 
class of salts present. Our alkalis consist of sulfates and chlorids, the 
carbonates being very subordinate in quantity. Sometimes the sulfates, 
sometimes the chlorids, and at other times the nitrates are the predom¬ 
inating salts in the water-soluble portions of these brown spots. For 
example we have sulfates 90.0, nitrates 8.2 and chlorids 1.5 percent; 
again nitrates 50.2, chlorids 38.2, and sulfates 9.9 percent; again nitrates 
35.6, chlorids 33.6, sulfates 28.3 percent; again chlorids 67.4, nitrates 
15.4, sulfates 15.1 percent; again sulfates 46.9, nitrates 41.9, chlorids 
10.0 percent; again sulfates 80.4, nitrates 15.1 and chlorids 4.1 percent. 
The last sample given is the extract from a gypsiferous, clay soil, and 
calcic sufate was the only sulfate present. Our ordinary white alkali 
is essentially a mixture of sulfates, but occasionally is very rich in 
chlorin. It seldom carries more than a trace of nitric acid and is often 
entirely free from it. I have, when possible, given the nitric acid as sodic 
nitrate. This, as elsewhere stated, has been done as a matter of con¬ 
venience. The nitrates present in some cases are certainly those of cal¬ 
cium and magnesium and these salts are probably always present but 
not necessarily to the exclusion of other nitrates. 
The fact of the existence of these spots is no longer in question, nor 
are the results due to their formation. The extermination of vegetation 
in these areas, involving the killing of many acres of old, well established 
apple orchards, has been observed in many places, and there is no question 
but that the nitrates are the cause of this. This question was naturally 
the first one suggesting itself. Neither the sulfates nor the chlorids 
produce the changes in the trees observed in these cases and nitrates do. 
The trouble complained of is characteristic and is common to all the 
cases that we have observed. 
The origin of these nitrates, however, may be questioned. The first 
explanation offering itself was that of concentration. In this event water 
seemed to be the only possible carrier. Our irrigating waters do not 
carry nitrates, for the most part they are snow-waters; our ground-waters 
do not carry greater quantities of nitrates than may be found in drain- 
waters from other lands, the same is true of our drain-waters unless they 
be from badly affected areas. Our well waters are not richer in nitrates 
than it is usual to find such waters. I have given in Bulletin 178 analyses 
of two most extraordinary well waters which contain nitrates. Our soils 
are not rich in organic matter or as a rule in nitrogen so that ordinary 
nitrification and leaching cannot account for it. Seepage and ground- 
waters may be very heavily charged with alkalis but ordinarily contain 
