BACTERIA OF OLD SOILS 



109 



powers. The results on ammonification compare well with others 

 secured from fresh soils, indicating that drying has little dele- 

 terious effect. 



NITRIFICATION 



Although recent work-^ has shown that many plants are able 

 to assimilate various forms of nitrogen other than nitrates, and 

 perhaps do so to best advantage, yet under field conditions and 

 for most agricultural plants there is not sufficient evidence in 

 hand to disregard nitrification as an essential soil function. It 

 appeared of interest therefore to determine the remaining nitri- 

 fying power of the soils. Upon suggestion of Dr. Lipman, in 

 order to avoid possible contamination likely to occur in using 

 glass tumblers, 25 grams of each soil were weighed into ster- 

 ile cotton stoppered flasks. A sufficient amount of a sterile 

 (NH4)2S04 solution of known strength was added to each flask 

 to add 0.1 gram of (NH4)2S04 to the soil. Three cubic centi- 

 meters of sterile distilled water was then added from a sterile 

 pipette and the flasks were incubated for two and a half weeks, 

 meanwhile keeping the water constant by further additions of 

 sterile distilled water. Duplicates and sterile controls were also 

 run on each soil. The nitrates were determined by the usual phe- 

 noldisulphonic acid method. Simultaneous qualitative ammonia 

 and nitrite tests were made. The results are recorded in table 3. 



TABLE 3 



NO. OF SOIL 



Mg. OP N AS 



NITRATES 

 ORIGIN.\LLY 

 PRESENT IX 

 SOIL 



Mg. OF N AS 



NITRATES 

 FOCND 



Mg. OP N AS 



NITRATES 

 FORMED 



NHi 



TEST 



NO2 

 TEST 



1 



0.560 



0.210 



- 0.350 



+ 



trace 



2 



2.000 



2.080 



+ 0.080 



+ 





3 



0.200 



0.136 



- 0.064 



+ 





4 



trace 



trace 



0.000 



+ 





5 



none 



none 



0.000 



+ 





6 



trace 



0.350 



+ 0.350 



+ 



+ 



7 



trace 



0.070 



+ 0.070 



+ 





8 



trace 



trace 



0.000 



+ 



+ 



9 



trace 



0.216 



+ 0.216 



+ 



+ 



Plus sign (+) denotes easih* detected quantities present. 



Minus sign ( — ) indicates insufficient amounts to affect the reagents used. 



" Jour, of Agri. Science 4: no. 3, p. 282. 



