Ba 2. 1:—646. 
BAC UERIOLOGICAL STUDIES OF THE SOILS OF THE 
TRUCKEE-CARSON IRRIGATION PROJECT. 
INTRODUCTION. 
In making a bacteriological study of any soil or group of soils there 
are certain fairly well defined groups bf micro-organisms whose func- 
tions, although as yet imperfectly understood, are recognized as im- 
portant factors in crop production and are more or less familiar to 
everyone who has attempted to investigate the problems of soil 
fertility. These groups of micro-organisms may be roughly separated 
into four classes, depending upon their physiologic characteristics: 
(1) Parasites, or organisms important chiefly because they are patho- 
genic to animals or plants and are frequently found in soils; (2) the 
cellulose-destroying organisms; (3) the organisms associated with the 
formation of humus; and (4) the organisms associated with the trans- 
formation of soil nitrogen. Only those groups concerned with the 
transformation of nitrogen, which in the form of ammonia or nitrate 
is practically the most important of all plant foods, are reported upon 
at this time. 
The data sought in studies of this character may be outlined as 
follows: 
(1) Total numbers of saprophytic bacteria in measured quantities of soil. 
(2) Ammonification; the breaking down of nitrogenous organic matter into ammonia. 
(3) Nitrification; the oxidation of various compounds of nitrogen to nitrate. 
(4) Denitrification; the reverse of nitrification. 
(5) Nitrogen fixation, symbiotic and nonsymbiotic; the utilization of atmospheric 
nitrogen in forming nitrogenous organic compounds. 
In the work conducted at Fallon, Nev., during the season of 1909, 
in cooperation with the Office of Western Agricultural Extension, no 
quantitative study was made of nitrogen fixation, and the data on the 
subject of ammonification are very meager. Some preliminary inves- 
tigations in arid regions had shown that nitrification takes place here 
at considerable depth. All studies, therefore, were made of a 3-foot 
zone, keeping separate the samples of soils from different depths. 
The comparative nitrifying power of the different samples from the 
various plats is shown by curves, the parts per million of nitrogen as 
nitrate and nitrite being plotted as ordinates, and the different depths 
as abscisse. These curves show only the gain in nitric and nitrous 
nitrogen. Chlorids and sulphates are also shown, but seem to be of 
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