MANGANESE 143 



iron sulphate influences the phosphorus metabolism of the plant. 

 It is hard to see how this is possible unless it be that the iron stimu- 

 lates the bacterial activity, which in turn liberates phosphorus 

 from its insoluble forms within the soil. It has already been noted 

 that Lipman found ferrous sulphate to have but little effect upon 

 nitrification, but his results were not conclusive. Guffroy found 

 sulphate of iron decidedly beneficial to oats, less beneficial to rye, 

 without action on rye-grass, and harmful to wheat. He concluded 

 that its action must be due to its influence on the biological processes 

 of the soil. According to Paterson and Scott, ferric hydrate has a 

 distinctly beneficial effect upon nitrification. In this latter case 

 its action could be due to its serving as a base. According to 

 Lipman and Burgess the ammonifiers are more sensitive to iron 

 sulphate than are the nitrifiers, for though small amounts of iron 

 sulphate stimulated the latter, it was toxic to the former in all con- 

 centrations tested. 



Magnesium Salts. Magnesium compounds usually stimulate 

 bacterial activities to a greater extent than do calcium compounds, 

 as has been noted in some of the literature already cited, Eng- 

 berding's results, however, showed that, while magnesium sulphate 

 stimulated bacterial activities, it was not as effective in this regard 

 as was ammonium sulphate, sodium nitrate, or potassium sulphate. 

 The work of Makrinov is of interest since he found pure magnesium 

 carbonate a very suitable substance on which to grow the nitrous 

 organism. Furthermore, magnesium carbonate had a strongly 

 beneficial effect on the physiological action of the organism. Keller- 

 mann and Robinson, on the other hand, found that magnesium car- 

 bonate when applied to a soil already rich in magnesium carbonate 

 positively inhibited nitrification if the quantity added exceeded 

 0.25 per cent. This is an apparent contradiction, but it may be 

 due to the different conditions of the experiments, since one investi- 

 gator was working with culture of the organisms whereas the other 

 was using the soil with its complex flora. Furthermore, it is quite 

 possible that magnesium carbonate may be without effect upon or 

 even accelerate the growth and activity of the Nitrosomonas and 

 yet inhibit the Nitromonas. 



Manganese. Some experiments by Skinner and Sullivan demon- 

 strate that manganese acts in various ways as a fertilizer. It is 

 often without influence, occasionally injurious, but usually bene- 

 ficial, its effect depending apparently upon the composition and 

 character of the soil. The oxidation in soils under treatment with 

 manganese salts was also studied and it was found that an increase 

 in oxidation and growth frequently occurred in aqueous extracts of 

 poor, unproductive soils. Although oxidation was increased in 

 fertile soils, growth was decreased, the plants showing indications 

 of excessive oxidation. Field experiments showed practically no 



