SOILS — FERTILIZERS. 217 



laboratory. In adclitiou, a series of cropping exporiuifuts was conducted to 

 determine (1) the influence of sterilized soils on tlie development of plants 

 and (2) the proportions of nitrogen and phosphoric acid most favorable for 

 plant development. Studies were also made of the relation of nitrogen and 

 phosphoric acid to soil fertility. 



The fixation of nitrogen by soil bacteria was found to depend on the cultural 

 condition of the soil, the intensity of the process increasing with the degree of 

 culture. It was higher in spring (tilled) fallow soil than in untilled. and 

 higher in the surface soil than in the subsoil of all the soils tested. 



Determination from time to time of nitric nitrogen in soil and subsoil indi- 

 cated that the intensity of nitrilication was much less in the cultivated top soil 

 tlian in the subsoil of both tilled and untilled fallow except for a few days at 

 the beginning of the tests, while the opposite was true of denitrification. 

 Studies of the processes of nitrification and denitrification in identical samples 

 of soil, however, indicated that when conditions were made favorable in the soil 

 for the growth and activity of nitrifying bacteria a medium was formed with the 

 resulting nitrates which was favorable to the growth and activity of denitri- 

 fying bacteria which in turn destroyed the nitrates already formed. It was 

 further found that some of the nitric nitrogen formed was converted into 

 albuminoids or into gaseous nitrogen. Some of the latter may be fixed by 

 nitrogen-fixing organisms and pass into complex organic forms. 



In addition to the results obtained in the preceding year in regard to the 

 chemical and microbiological fixation of soluble phosphoric acid (E. S. R., 28, 

 p. 417) it was found that the fixation of easily soluble phosphoric acid depends 

 t;s much on chemical as on biological factors, and the intensity of this process 

 depends directly on the cultural condition of the soil. The total fixation 

 through both chemical and microbiological factors was found to be greater in 

 subsoils than in cultivated top soils as was also the case where the fixation 

 was due to chemical factors alone, but when due to microbiological factors 

 alone the intensity was found to be the greater in the top soil. 



Sterilization of soils with chloroform and with heat, as previously noted, 

 increased the crop yield by converting the phosphoric acid and nitrogen into 

 available forms. The crop yield increased with the nitrogen added; but with 

 increased phosphoric acid there was first an increase, then a decrease. In- 

 creasing both fertilizers slightly increased the crop. 



Fallow soil was found to be in the best physical and chemical condition, and 

 phosphoric acid was more needed as a fertilizer in this soil than nitrogen, 

 although both are considered indispensable in raising the soil to a high degree 

 of fertility. 



Bacterial action in the soil as a function of food concentration and of 

 insoluble org-anic substance, O. Rahn {Centbl. Bakt. [etc.'\, 2. Abt., 38 {1918), 

 No. 19-20, pp. 484-494). — This work is a continuation and completion of studies 

 previously noted (E. S. R., 29, p. 817), and is devoted chiefly to a study of the 

 influence of porous spongy substances, such as cellulose, on bacterial activity in 

 soils. Cellulose in the form of finely grated filter paper was mixed with sand, 

 washed with hydrochloric acid, in different proportions. These mixtures and 

 likewise sand without cellulose were moistened with a 5 per cent peptone solu- 

 tion, and a peptone solution without sand addition was also used in each series. 

 These different combinations were sterilized in the autoclave and inoculated 

 with a culture of Bacillus mycoides. The cultures were analyzed after 2, 4, 6, 

 10, and 20 days' incubation and the progress of decomposition and the different 

 speeds of transformation in the individual combinations noted. The influence 

 of the concentration of peptone and of variations in water content and of cellu- 

 lose on the ammonification are specially noted. 



