Soil, Changes Produced By Micro-organisms. 25 
that an abundant supply of organic matter in the soil is one of the 
requirements for active nitrogen fixation. 
A careful study of some thirty Colorado soils was made by 
the writer over three years ago, for the purpose of learning whether 
there was any relation between the high nitrate content of these 
soils and soil bacteria. The samples collected represented orchard 
land, raw land, beet, alfalfa, and grain fields, and truck gardens. 
It was suspected that possibly Azotobacter, favored particularly by 
the alkaline reaction of the soil, was fixing immense amounts of 
nitrogen as protein, which was subsequently converted into nitrates 
by ammonification and nitrification. This question is of tremendous 
economic importance since the amount of niter in some localities is 
approaching 100 tons per acre foot, and all kinds of vegetation are 
dying as a result of the accumulation. In describing the serious 
condition brought about by this trouble, I can do no better than 
to restate what I have said on this subject in a former bulletin. 
“Somewhat over a year ago, Dr. Headden called my attention 
to the extremely large quantities of nitrates present in certain Col¬ 
orado soils, stating at the time that these nitrates were frequently 
associated with a brown discoloration of the soil, and that this color 
was often confined to well defined areas varying in size from three 
feet in diameter to an acre or more; furthermore, that these so called 
“brown spots” were not fixed, inert quantities related to some 
recognized geological formation, but that they were alive, and in 
the process of making as evidenced not only by the rapid progress 
with which the then existing spots were spreading, but also by the 
almost continual appearance of new spots both in old and new 
localities. 
Dr. Headden has been studying our alkali soils and drainage 
waters for the past sixteen years, and he tells me that complaints of 
“brown spots on which nothing will grow” have been common, but 
more so during the past five years; reports have been received from 
the cantaloupe growers that their melons are deteriorating in quality 
without any assignable cause ; truck gardens, alfalfa, oat, barley and 
sugar beet fields have been developing barren patches where a uni¬ 
form stand was always obtained in former years; in some parts of 
the state, the sugar content of the sugar beets as well as the purity 
and tonnage have fallen off until it is a ponderous question with the 
farmers and sugar factories whether the growing of sugar beets 
in those localities is any longer a profitable industry; but equally 
serious, if not even more so than any of these, is the destruction 
which is being wrought in some of the apple orchards'of Colorado. 
