98 ABSTRACTS 



The Indirect Effect of Certain Soil Treatments Upon Bacterial Activity. 



P. L. Gainey. 



Different methods of preparing seed beds for winter wheat at the 

 Kansas Station have given very large differences in the accumulation 

 of nitrate nitrogen prior to seeding. Early (July 15) versus later, and 

 deep (eight inches) versus more shallow plowing, have given higher 

 nitrate contents. Efforts to trace observed differences to variations 

 in bacterial flora have failed. Evidence was presented showing a cor- 

 relation between moisture content of the surface soil and nitrate ac- 

 cumulation. A summary of data accumulated indicates that the 

 various treatments have had but slight effect upon the organisms con- 

 cerned in nitrate formation, except in so far as this activity is controlled 

 by other factors. 



Studies on Soil Protozoa and their Relation to the Bacterial Flora. J. M. 



Sherman. 



The occurrence and activity of protozoa in soil. The results obtained 

 from sixteen fertile soils representing various soil types indicate that 

 these soils contain about 10,000 protozoa per gram. The predominating 

 protozoa in the soils studied were flagellates. Ciliates and amoebae 

 were occasionally found in numbers approximating 1,000 per gram. 



It was demonstrated that certain types of flagellates are capable of 

 multiplication in soil. The ciliates which were tested were not able 

 to increase in soil when kept at its normal moisture content. 



The effect of protozoa upon the soil bacteria. Observations made on 

 soils containing protozoa and free of protozoa, at various temperatures, 

 with different moisture contents, and on various types of soil indicated 

 that the protozoa in the soils studied did not have a limiting action upon 

 the bacterial flora. 



The effect of specific types of protozoa, in animal-pure cultures, 

 upon the soil bacteria was also studied. The ciliates limit the develop- 

 ment of bacteria markedly in soil extract, but are not able to exert this 

 effect in soil, since they do not lead a trophic existence under ordinary 

 soil conditions. 



Of four types of active soil flagellates which were tested three had 

 no apparent effect upon the number of bacteria, either in soil or in 

 soil extract. The fourth organism, a species of Monas, had a marked 

 limiting action upon the bacterial flora in soil extract but apparently 

 had no effect in soil. 



The effect of volatile antiseptics upon the soil micro-organisms. The 

 treatment of soil with volatile antiseptic does not free it of protozoa. 

 The active soil protozoa again multiply and attain their normal num- 

 bers within one month after treatment. 



The maximum numbers of bacteria in partially sterilized soils are 

 not found while the protozoa are suppressed, but after these organisms 

 have again reached their maximum numbers. 



The number of bacteria in treated soils cannot be decreased by rein- 

 oculation with one per cent of untreated soil. 



