Aug. 1909.] Soil Bacteriology. 241 



By comparing tables I to X in the preliminary experiments 

 (part I), it was found that the total number of bacteria in the 

 surface foot of soil is increased by the deeper plowing. This 

 fact is also shown in tables IX to XII (part II) , which contain 

 the sum totals of tables V to VIII. In the Marshall silt loam 

 there was also a slight advantage in regard to the total num- 

 ber of bacteria in favor of the plots which were replowed on 

 June 20. 



AMMONIA PRODUCTION. 



Tables XIII to XVI show the relative amounts -of ammonia 

 produced in the different plots. The total amount produced in 

 the silt loam soil exceeded that produced in the sandy loam 

 soil. A comparison of the tables will show that the amount of 

 ammonia produced in the different plots, both in the sandy 

 loam and the silt loam, increased with the depth of plowing. 

 The depth of plowing seems to have greater effect upon the 

 ammonia production in the more tenacious silt soil." 



This increase in ammonia production was not regular, but in 

 general conformed to the depth of stirring, although the 

 amount produced varied greatly from week to week. Excess 

 of moisture showed a tendency to lessen the amount of am- 

 monia produced. 



Occasionally only a trace of ammonia was present, as will be 

 seen in table XIII, subplot A4, on July 20, and again in sub- 

 plots A3 and A4, on August 17. This irregularity is found in 

 all the plots. In many cases where these low yields occurred 

 the medium was overgrown with an organism which produced 

 a greenish pigment similar to that of Ps. fluorescens liquefa- 

 ciens. These bacteria seemed to predominate during an ex- 

 cessively moist period. 



REDUCTION OF NITRATES. 



Denitrification, or the reduction of nitrates to nitrites, with 

 the final liberation of nitrogen gas, may accompany the de- 

 structive processes of nitrogen compounds. Some of the am- 

 monia compounds are broken down, liberating free nitrogen, 

 while at the same time the nitrates which may have been 

 formed are reduced to nitrites. These may be broken down 

 into simpler substances, thus releasing free nitrogen. 



The results of the experiments testing denitrification are 

 given in tables XIII to XVI, under the heading "Nitrites," ex- 



