1 



Soil Organisms concerned in Nitrogen Cycle. 519 



organic substances is favourable to nitrification in impure culture, and that 

 especially good effects are produced by humates in very small amounts. 



In order to examine the effect of bacterised peat upon nitrification in soil 

 a preliminary experiment was carried out upon a rich garden soil from Kew. 

 Four portions of soil, each weighing 24 oz., were taken, and each of two 

 of them was mixed with one part in ten by volume of bacterised peat. 

 Two portions of another soil were also taken, one being treated and the 

 other serving as control. Three samples of each were weighed out for 

 nitrate determination, and the six soils were kept in wide-mouthed glass 

 bottles at about 20° C. as before. They were aerated daily, and the 

 moisture content kept as uniform as possible. At intervals they were all 

 examined for nitrate, the determinations being made by the phenol-sulphonic 

 acid method. The figures obtained by this method were very concordant, 

 and at the outset a comparison was made between the results thus obtained 

 and those given by the method of reduction by sodium amalgam, the 

 ammonia being separately determined when the latter process was adopted. 

 A close agreement was shown between the figures, and the more cumbersome 

 sodium amalgam method was therefore discarded. 



When dealing with solutions containing the water extract of the peat, the 

 deep colour could readily be discharged by precipitating the humic acid with 

 a drop of dilute hydrochloric acid and shaking the filtrate with carbon 

 black (D. Elf brand). The colourless liquid thus obtained was then 

 analysed, and concordant results obtained by this method of procedure. 



The figures obtained at intervals from the above soils were : — 



Table VI. 





Nitrate content (parts per million of nitric nitrogen — 

 mean of three determinations). 





Originally. 



After 

 7 days. 



14 days. 



21 days. 



28 days. 





30 



43 



57 



107 



20S 



2. „ 



31 



45 



56 



112 



200 





35 



45 



81 



95 



99 



4. Soil A + bacterised peat 



^* >) ») » - 

 6. Soil B + bacterised peat ... 



* 



27 

 29 

 30 



87 

 91 

 156 



450 

 439 

 248 



540 

 528 

 319 



539 

 541 

 372 



Each of the figures in the above and following Tables of soil analyses 

 represents the mean of three determinations, the maximum deviation from 

 the mean being +5. 



The fact that the increase in nitrate content in the soils A containing 



