620 EXPERIMENT STATION RECORD. [Vol 40 



that of atmosphere. Oxygen decreases during the period of active nitrification ; 

 that is, during the warmer season of the year. There are times at which the 

 soil air may be entirely deprived of oxygen. Variations in atmospheric pres- 

 sure, velocity of the wind, and temperature, as well as of the crop, appear to 

 have some effect on the composition of the soil air. 



Layer formation in soil suspensions, P. Ehrenbebg, E. Haiix, and O. Xolte 

 (Zentbl. Agr. Chan., 1,7 (1918), No. 6, pp. 145-147). — Observations made upon 

 the formation of layers in suspensions of clay and heavy arable soils led to the 

 conclusion that the size, form, weight, and electrical charge of the soil par- 

 ticles were the principal factors involved. Layer formation is said to have 

 occurred only where definite groups of particles were present which differed 

 in the velocity with which they settled out of suspension. Neither temperature 

 nor light appeared to have any significant Influence upon the phenomenon. 



The Nile silt (Rev. Sci. [Paris], 57 (1919), Xo. 3, p. 87).— It is stated that 

 the deposit of silt amounts to 15 tons per hectare (6 tons per acre) annually, 

 containing sufficient fertilizing constituents to compensate tor the removal of 

 such constituents in the crops. The proportion of phosphoric acid is 2 parts 

 per thousand, of potash 6 to 7 parts, and of lime 3.3 per cent. Recent studies 

 have shown also that the silt is rich in active microorganisms, which contribute 

 largely to the beneficial effect of the silt. The silt may therefore be considered 

 a living fertilizer. 



A study of the indigo. soils of Bihar. YV. A. DAVIS I Igr. !'• Search Inst. Piisa 

 Indigo Pub., 1 (1918). pp. 75; abs. in Nature [London). 208 (1918), \" 1550, 

 pp. 27, 28). — From observations of soil conditions as determined by chemical 

 analysis, the author concludes that the yield of Indigo varies directly with the 

 amount of available phosphoric acid present in the soil and subsoil, and that 

 soil improvement through the use of superphosphate is the most Important 

 factor in the successful production of natural Indigo. 



The role of bacteria in relation to phosphates In the soil is briefly described 

 by C. M. Hutchinson. 



Nitrates, nitrification, and bacterial contents of five typical acid soils as 

 affected by lime, fertilizer, crops, and moisture. H. A. NOTES and S. 1 ». Con- 

 ner (Jour. \</r. Research [V. S.], 16 (1919\. No. -'. pp. 87-48, pis. 9. rigs. 8).— 

 In the investigations at the Indiana Experiment Station, here reported, con- 

 trolled greenhouse experiments were conducted on five typical acid soils in 

 order to ascertain the variations in bacterial numhers. nitrates, and nitrifica- 

 tion under different conditions and treatment. "In part of the experiments 

 the soils were fertilized with calcium carbonate, add phosphate, ami complete 

 fertilizer, cropped to wheat and clover and kept at optimum moisture content, 

 while in another series the soils were unfertilized, oncropped, and kept one- 

 fourth, one-half, and fully saturated with water. 



"The results reported Include crop yields, soil-acidity determinations, nitrates 

 in the soil when sampled and after lncuhation with ammonium sulphate, and 

 ajso the numbers of aerobic, anaerohic, and carbon-dioxld surviving micro- 

 organisms present in the soils. 



"All the untreated soils were quite acid and contained nitrates when sampled, 

 showing that nitrification takes place In acid soils. The amounts of nitre 

 present and the nitrifying power of the untreated acid soils varied with the 

 organic matter and total nitrogen rather than with the soil acidity. Calcium- 

 carhirnate additions markedly increased the nitrification of all live soils. Fer- 

 tilization tended to increase nitrification, hut not so much as calcium carbonate 

 did. Regardless of treatments the presence of growing clover kept down 

 nitrate contents of the soils. The degree of saturation of the soils alio, ted the 



