6i2 Journal of Agricultural Research voI.xv.no.h 



ulation in the air-dry soil. For the soil containing lo per cent of water 

 5 cc. of carbon disulphid and i cc. of toluol were sufficient to destroy 

 Azotobacter, while 5 cc. of either were sufficient to check nitrate accum- 

 ulation; 0.5 cc. of toluol checked Azotobacter in one sample, but 

 was not sufficient to kill. The results for the soil containing 20 per cent 

 of water are in every respect similar to that containing 10 per cent. 

 In all cases there was an accumulation of ammonia only when nitrifi- 

 cation was checked. 



The only air-dry samples in which carbon disulphid destroyed Azoto- 

 bacter were those treated with 10 cc. In one unevaporated sample 

 5 cc. eliminated Azotobacter, although in the dupHcate no elimination 

 occurred. Ten cc. checked the nitrate accumulation in unevaporated 

 samples, but were ineffective where the carbon disulphid was evapor- 

 ated. 



When the water content was 12 per cent, 5 cc. of carbon disulphid 

 were sufficient to destroy Azotobacter and to check nitrate accumu- 

 lation. This also is true of the soil containing 24 per cent of water. 

 Where the water content was 36 per cent, the results are somewhat 

 irregular. Azotobacter were destroyed and nitrate accumulation was 

 checked when treated with 5 cc; however, 0.5 and i.o cc. appeared 

 to aflFect the Azotobacter in one instance each, but was without effect 

 upon the nitrate accumulation. This irregularity was probably due 

 to reinoculation in the case of those samples in which duplicates did 

 not agree. The results agree in showing an accumulation of ammonia 

 only in those samples in which nitrification was checked. 



The results with toluol as given in Table VI show that in the air-dry 

 soil 5 cc. were sufficient to destroy Azotobacter in the nonevaporated 

 samples, while 10 cc. were insufficient in the evaporated samples. Appar- 

 ently nitrate accumulation was checked to an appreciable extent with 

 10 cc. in nonevaporated samples, but was not affected when the toluol 

 was evaporated from the soil. One cc. of toluol was sufficient to des- 

 troy Azotobacter in evaporated and in one nonevaporated sample 

 when the water content was 12 per cent, while 5 cc. were required to 

 affectively check, nitrate accumulation. -In one evaporated sample 

 I cc. checked the nitrate accumulation. 



When the moisture content was raised to 24 per cent, i cc. destroyed 

 Azotobacter in all samples, while 5 cc. were still required to check 

 nitrate accumulation to any appreciable extent. 



With a moisture content of 36 per cent, 0.25 cc. of toluol destroyed 

 Azotobacter, and i cc. was sufficient to check nitrate accumulation. 

 As in all other experiments ammonia accumulated only when nitri- 

 fication had been checked. 



It appears from these results that both carbon disulphid and toluol 

 will check nitrate accumulation if applied in sufficient quantities. The 

 quantity necessary to bring about this effect varies quite widely with 

 the physical condition of the soil and probably also with different soils. 



