134 BIOLOGICAL CONDITIONS OF THE SOIL 



nitrogen. Some soil students go so far as to say that an 

 important part of the injury to crop production on alkali 

 lands is due to decreased bacterial activity. They hold 

 that this is shown by the fact that crop yields do not 

 always decrease to the full extent when alkali is first brought 

 in contact with the soil, but continue to decrease as time 

 allows the microorganisms to die gradually. They also 

 point out that soils do not become at once productive after 

 being drained of alkali, but gradually increase in productive- 

 ness as the desirable organisms are given time to multiply. 

 Whether the changes which soils undergo subsequent to 

 drainage are due largely to bacterial activities or almost 

 wholly to physiological changes is not at present known. 



From preliminary experiments by Lipman and 

 Fowler (13) in which soils were treated with 500 parts per 

 million of sodium carbonate, 1000 parts per million of 

 sodium chloride, 2500 parts per million of sodium sulphate 

 and mixed salts, and then leached free of the salts, it was 

 found that nitrification was affected profoundly by the 

 leaching. The characteristic effects of the salts on the 

 organisms remained after the salts had been almost en- 

 tirely leached out. The soil receiving the mixed salts 

 was most toxic, with sodium carbonate, sodium chloride, 

 and sodium sulphate in the order named. This same action 

 was noted for the nitrogen-fixing bacteria, although it 

 was not so characteristic as with the nitrifying ones. The 

 results with the ammonifiers was not so distinctive. 



Barnes and AH (i) found that the ammonifying bac- 

 teria, and to a less extent the nitrifiers, might be used to 

 measure the toxicity of the alkali or its crop-producing 

 power much more quickly and at less expense than by 

 growing crops. They believe that the alkali merely causes 

 the organism to lie dormant until favorable conditions 



