THE EFFECT OF CYANAMID AND RELATED COMPOUNDS 
ON THE NUMBER OF MICROORGANISMS IN SOIL 1 
By F. E. Allison 
Soil Biochemist, Fixed Nitrogen Research Laboratory , United States Department 
of Agriculture 
INTRODUCTION 
The decomposition of cyanamid in soil is directly dependent in certain stages 
of the process upon the numbers, species and efficiency of the soil microorganisms 
in bringing about the desired changes. The conversion of calcium cyanamide 
into acid cyanamide, then free cyanamide and the latter into urea is thought to be 
chiefly a series of chemical changes in which soil colloids play an important 
role. The conversion of urea into ammonia and the oxidation of the latter to 
nitrites and nitrates are biological phenomena. It is, therefore, important to 
know the effect of cyanamid and its possible transformation products upon the 
numbers of soil organisms. It was with this idea in view that the experiments 
reported below were undertaken. 
EXPERIMENTAL 
Five groups of experiments were carried out at intervals lasting over a period 
of about 18 months. The methods used in the first of these were considerably 
different from the later work and are, therefore, discussed separately. 
EFFECT OF CYANAMID AND OTHER NITROGENOUS COMPOUNDS ON 
BACTERIAL NUMBERS 
A Susquehanna loam soil of relatively high fertility was secured from a garden, 
sieved while moist, and spread out in a thin layer to dry where not exposed to 
direct sunlight. Sixteen samples of 500 gm. each were than weighed out into 800 
cc. beakers. To each was added 5 gm. of precipitated calcium carbonate and 
the different nitrogenous materials shown in Table I, these materials being 
uniformly mixed with the soil. The optimum moisture content of the soil was 
then determined and this quantity, 21.5 cc. of water per 100 gm. of soil, was 
added regardless of treatment. It was realized that the actual quantity of 
available moisture would be less in the soil receiving cyanamid, because of its 
drying properties, but it was decided not to make a correction for this factor. 
During the incubation period, which began on February 5, 1921, the beakers 
were kept covered with watch glasses and maintained at room temperature. 
Water was added at frequent intervals to replace that lost by evaporation. 
The first samples for analysis were taken from the center of the beakers at 
the end of 16 days by means of a sterile cork borer, having a diameter of about 
three-fourths of an inch. These soil samples were added to flasks containing 
sterile tap water, then shaken at intervals covering a period of a half hour and 
agar plates poured according to the usual bacteriological technique. 
1 Received for publication April 28,1924—issued Nov., 1924. 
Journal of Agricultural Research, . Vol. XXVIII, No. 11 
Washington, D. C. June 14,1924 
Key No. R-3 
( 1159 ) 
