SOILS — FERTILIZERS. 423 



Azotobacter, namely, aeration, the presence of lime and of available carbo- 

 hydrates, and the maintenance of the supply of organic matter. 



The nitrogen cycle in nature, K. Kaiser (Gartenflora, 64 {1915), Xos. 5-6, 

 pp. 73-So, figs. 3; 7-8, pp. 113-123, figs. 2). — This article discusses the nitrogen 

 cycle in its relation to the physiology of plants and animals ; the history of and 

 the processes involved in the Chile nitrate, ammonium sulphate, and other 

 nitrogen fertilizer industries ; and the processes of nitrogen fixation, nitrifica- 

 tion, and denitrification in soil. 



The manurial value of natural (dried) and of degreased sewage sludge, 

 J. A. VoELCKEE {Rpt. Comrs. Treating and Disposing of Seivage [Gt. Brit.], 9 

 {1915), pp. 156, 157; abs. in Jour. Bd. Agr. iLondon], 22 {1915), No. 3, pp. 235- 

 238). — Pot experiments are reported with wheat on a light sandy loam soil 

 deficient in lime to determine the fertilizing value of sewage sludges, obtained 

 from seven different processes, when in the natural (dried) state and when 

 the gi-ease had been extracted. 



Analyses of one sample each of the natural and degreased sludges showed 

 that they contained, respectively, 2.49 and 3.02 per cent lime, 0.69 and 0.64 

 per cent phosphoric acid, 2.01 and 1.77 per cent total nitrogen, and 7.58 and 1.9G 

 per cent ether extract. The sludges were added at the rates of 1 and 2 tons 

 per acre and 1 ton per acre supplemented by i ton of lime. 



Both types of sludge produced an increase in the yield of wheat, the gain 

 • being more marked in the grain than in the straw. " The best results were 

 obtained by the use of sludge, whether natural or degreased, along with 

 lime. . . . One ton per acre of the natural sludge used alone did considerably 

 better than a corresponding 1 ton of the degreased, but between the 2 tons 

 per acre application of each the difference was small, the 1 ton per acre of 

 natural sludge along with lime doing, however, rather better than a similar 

 application of degreased sludge with lime. . . . There would appear, there- 

 fore, to be no advantage, from a manurial point of view, but rather the reverse, 

 in the degreasiug process." 



Comparative field trials with dried and degreased sewage sludges at 

 Rothamsted, E. J. Russell and E. H. Richards {Rpt. Comrs. Treating and Bis- 

 posing of Seivage [Gt. Brit.], 9 {1915), pp. 158, 159; abs. in Jour. Bd. Agr. 

 [London], 22 {1915), No. 3, pp. 235-238). — Field experiments with grass and 

 oats on a heavy loam soil to determine the fertilizing value of dried and de- 

 greased sewage sludges are reported. 



Analyses of one sample each of the dried and the degreased sludges showed 

 that they contained, respectively, 1..53 and 1.55 per cent nitrogen, 0.85 and 1.33 

 per cent phosphoric acid, and 8.55 and 1..57 per cent ether extract. 



The results of the experiments showed that neither of the sludges gave any 

 marked return or pos.sessed any manurial value when used alone in quantities 

 up to i ton per acre. It is concluded that the nitrogen in sewage sludge is in 

 a very stable combination which does not decompose readily under natural 

 soil conditions, and that the removal of fat does not increase the ease of de- 

 composition. 



The Dickson centrifuge system of sewage treatment, E. H. Teipp {Jour. 

 Soc. Chem. Indus., 34 {1915), No. 10, pp. 517-524, figs. 7). — In connection with a 

 discussion of a process consisting mainly of treating sewage with live brewers' 

 yeast, it is shown that the resulting sludge contains less water and more organic 

 matter and total nitrogen than ordinary septic tank sludge and a relatively high 

 content of nitrogen available to plants. 



Analyses of two samples of the dried sludge showed that they contained, 

 respectively, 46.79 and 47.85 per cent organic and volatile matter, 28.13 and 

 28855°— No. 5—16 3 



