622 EXPERIMENT STATION EECORD. 



It was found that the dilution method gives only relative, not absolute, re- 

 sults, and that the whole of the protozoa in soils do not develop in soil extract. 

 In connection with the dilution method, heating to 58° C. appeared to kill a 

 number of the encysted protozoa in addition to active forms. Treatment with 

 caustic potash killed all active protozoa, but left the encysted uninjured. " It 

 is evident that it is impossible to fix upon a temperature which will destroy all 

 active protozoa in soils and leave the cysts perfectly uninjured. ... As it is 

 better to select a temperature which will kill all active forms even if it does 

 injure some of the cysts, rather than one which will leave the cysts unharmed, 

 and also probably some of the active forms alive, the continued use of 58° C. 

 seems to be justified." 



Experiments on the effects of temperature and moisture on the soil protozoa 

 brought out " that some, at least, of the protozoa in soils lead an active life and 

 are capable of multiplying to quite a considerable extent when the conditions 

 become favorable." It was also found that the soil protozoa, in solutions, ex- 

 ercise a very decided limiting effect on the numbers of bacteria. 



The results obtained as regards the influence of protozoa on ammonification 

 in solution tests were inconclusive. 



The reduction in bacterial numbers in the soils inoculated with protozoa was 

 found to be very marked and to lie well outside the limits of experimental 

 error. " The conclusion may safely be drawn, therefore, that the limiting 

 factor, or at least one limiting factor (of Russell and Hutchinson) has been 

 inoculated into the sterilized soils and has produced its effects on the numbers 

 of bacteria. ... As it has been shown that the protozoa are capable of reduc- 

 ing the numbers of bacteria in solutions, it appears justifiable to consider them 

 as the limiting factor in soils." 



Studies on the lime requirements of certain soils, H. B. Hutchinson and K. 

 MacLennan {Jour. Acjr. 8ci. [England], 7 {1915), No. 1, pp. 15-105, pi. 1, 

 figs. 4)- — In continuation of work along the same general lines as that previously 

 noted (E. S. R., 32, p. 32), investigations are reported dealing with the deter- 

 mination of the amount of lime (CaO) necessary to induce partial sterilization 

 changes in soils and the amount of lime (CaO) or chalk (CaCOa) required for 

 soil neutralization. 



It was found that calcium oxid is capable of producing partial sterilization 

 effects but that calcium carbonate is not. The amounts of lime necessary to 

 produce specific effects in dilferent soils varied greatly, and the critical amount 

 required was foimd to depend on the amount necessary for the production of an 

 alkaline reaction of the soil water. The results obtained on this basis, cor- 

 related with those of pot experiments, showed that the amount indicated coin- 

 cides with that required for the maximum production of dry matter in the first 

 crop following treatment and the maximum production of dry matter in the 

 first four crops. Applications of lime double or treble the amount indicated 

 by the method, although causing an increase in the ammonia and nitrates pro- 

 duced, did not give corresponding increases in crop. Certain physical changes 

 also occurred about the partial sterilization point. 



The determination of the lime requirements of the soil was found to depend 

 on the absorptive capacity of the soil for calcium carbonate (present in solu- 

 tion as bicarbonate). Comparative tests of various soils to which quantities of 

 lime had been added previously showed a proportionate diminution of the lime 

 requirements, and no absorption was indicated in the case of neutral soils. Soils 

 showing a positive lime requirement according to this method were found to 

 respond distinctly to the application of carbonate by increased ammonia and 

 nitrate production in laboratory experiments and by greater plant growth in 



