1916] SOILS FERTILIZERS. 627 



had a neutralizing action upon the toxicity to bacteria of extracts of certain 

 soils, and this was traced to the free acid. . . . 



"Ammonification proceeded at the normal rate in soil under semianaerobic 

 conditions and was apparently not interfered with by the bacteriotoxins pro- 

 duced, although the activity of such ammoniliers as Bacillus mycoides is actu- 

 ally lowered by the presence of B. X. This latter organism does not appear to 

 be universally present in soils. No concentration of ammonia above that in the 

 aerated control was found, nor was this gas given off by the anaerobic soil." 



In a special experiment to test the action of the carbon dioxid formed in soil 

 by bacterial action upon nitrification in that soil, it was found that " under par- 

 tially anaerobic conditions absorption of the carbon dioxid produced no effect upon 

 nitrification in soil, eitlaer of oil cake or of ammonium sulphate. . . . Complete 

 nitrification of ammonium sulphate tools place under semianaerobic conditions 

 in which no nitrification of oil cake occurred. . . . 



" It was found that salts of some of the heavy metals, such as copper, had a 

 decided influence in neutralizing the toxic action toward seedlings of extracts 

 of soiLs kept under anaerobic conditions." 



In studies of nitrification " grass has been found to prevent entirely accumu- 

 lation of nitrate in the soil in which it is growing. . . . The optimum amount 

 of organic matter as oil cake containing 5 per cent of nitrogen for nitrification 

 in Pusa soil was found to be about 1 per cent of soil weight. . . . The effect of 

 temperature on nitrification in Pusa soil was tested, the optimum being found to 

 be near 35° C. (95° P.). No nitrate was formed at 40°, nor did nitrification 

 take place in soil which had been kept at 40°, when its temperature was after- 

 wards reduced to 30°." 



Experiments to determine the cause of the rise and sudden fall of the rate of 

 carbon dioxid evolution when solid bacterial foodstuffs are added to live soil 

 indicated that this result " was due in part to auto-intoxication by the soil 

 bacteria and in part to the purely physical facts of the case." 



The progress of green-manuring experiments and studies of Azotobacter, to 

 be reported on elsewhere later, is also noted. 



The humification of the constituents of plant organisms and the effect of 

 natural agents upon it, A. Tbusov (Trouseff) (Selsk. KJios. i lAesov., 2^7 

 {1915), Api\, pp. 575-605; abs. in Tniernat. Inst. Agr. [Rome^, Mo. Bui. Agr. 

 Intel, and Plant Diseases, 6 (1915), No. 11, pp. 1453, lJf54). — Separate studies 

 of the processes of decomposition of the different constituents of plant organ- 

 isms and of various mixtures of these constituents, including carbohydrates 

 with proteins, fats, pigments, tannic and encrusting bodies, gums, glucosids, 

 and organic acids, are reported in an effort to throw light on the genesis of 

 humus. Decomposition was studied both as it occurs on the soil surface and 

 within the soil. 



It was found that " lignin, proteins, starch, chlorophyll, tannic bodies, phlo- 

 baphenes, some fats, and gums are the direct sources of the humus formed 

 from plant residues on the surface of the soil. Cellulose, hemicellulose, mono- 

 saccharids and disaccharids, glucosids, and organic acids (including amido- 

 acids) do not give rise to humus under these circumstances. In view of the 

 considerable amount of proteins contained in bacteria, the possibility of the 

 ti-ansformation of the bodies of bacteria into humus may be admitted. In the 

 case of fungi this transformation has been confirmed. . . . 



"All the organic constituents utilized by micro-organisms for their nutrition 

 may, by means of their bodies containing nitrogen, become indirect sources of 

 humus. Typical black humus is rapidly formed only when all of the following 

 constituents together take part in its formation: Lignin, proteins, pigments. 



