620 EXPEEIMENT STATION EECORD. 



The effect of some organic soil constituents upon nitrogen fixation by 

 Azotobacter, H. S. Reed and B. Williams (Virginia 8ta. Tech. Bui. 4 (1915), 

 pp. 81-96; Centbl. Balct. [eic], 2. AM., J,S (1915), No. 1-7, pp. 166-176; 

 abs. in Science, n. ser., 42 (1915), No. 1079, pp. 320, 821).— The results of 

 a study of the effect of various organic compounds likelj' to be constituents 

 of the soil on the growth of Azotobacter are reported, which indicate that nitro- 

 gen fixation by these organisms was only slightly influenced by most of the 

 compounds tested. A depression was noted in a number of cases, but it was 

 usually the result of a relatively high concentration of the compound used. 

 Hydroquinone and salicylic aldehyde were the most toxic of any compounds 

 studied, while esculin, quinic acid, and borneol afforded marked stimulation to 

 the gi'owth of the organisms. In concentrations which are considered fatal to 

 certain higher plants many of the compounds only slightly depressed fixation. 



Such nitrogenous compounds as nicotin, picolin, guanidin, and skatol showed 

 toxic properties commensurate with those usually ascribed to these substances, 

 while caffein appeared to stimulate the growth of the organism. " Many of 

 the nitrogenous compounds used which have been reported as beneficial to 

 higher plants exercised a marked depression on fixation. It appears that the 

 simpler compounds were more pronounced in this respect than were the more 

 complex ones. It is suggested that this condition is not one of toxicity, but 

 that the nitrogen of the compounds was utilized by Azotobacter in preference 

 to that of the atmosphere. Urea, glycocoU, formamid, and allantoin were espe- 

 cially active in depressing fixation." 



A list of the organic compounds studied, showing their occurrence and pos- 

 sible source in the soil, together with reports on their action toward higher 

 plants and a list of references to literature bearing on the subject, are appended. 



Nitrogen fixation and nitrification in various soil types, H. S. Rekd and 

 B. Williams (Virginia Sta. Tech. Bui. S (1915), pp. 59-80).— This bulletin 

 reports in four papers experiments on the effect of mineral fertilizers on nitro- 

 gen fixation and nitrification in soil, nitrogen fixation and nitrification in 

 various soil types, and the effect of sand, and lime on nitrification. 



It was found that the various inorganic fertilizers did not cause marked 

 stimulation of nitrogen fixation in truck soils. The maximum fixation was 

 attained under the influence of stable manure with lime. 



Crimson clover increased the nitrifying power of the soil 83 per cent, crimson 

 clover and lime 526 per cent, stable manure 120 per cent, and stable manure 

 and lime 407 per cent. 



An examination of 93 soils, 88 of which were collected in pairs of virgin and 

 cultivated samples, showed the superiority of cultivated soils for nitrogen fix- 

 ation. Fixation by virgin clay soils was greater than by light virgin soils. 

 The results of these studies are taken to indicate that, with the possible excep- 

 tion of lime, the humus content of a soil and its cultivation are the only factors 

 which materially affect nitrogen fixation. 



In nitrification studies of the 93 soils, using ammonium sulphate solution, it 

 was found that cultivated soils showed decidedly higher nitrifying qualities 

 than the virgin soils. The nitrifying power of light open sandy soils was 

 strikingly low, that of loams and clay loams was the highest, and that of heavy 

 clays was also low, but not so low as that of the light soils. It is thought, 

 however, that the low nitrifying power of the heavy clays can be improved by 

 proper tillage. 



Studies of the soils with reference to their accumulation of nitrates over a 

 period of six months did not show the distinptive superiority of cultivated soils 

 over virgin soils, as was evinced in the ammonium-sulphate tests. The clay 



