SOIL PHYSICS, CHEMISTRY AND MICROBIOLOGY I415 



2nd. method. — In the series of experiments where germicides were 

 used, the same apparatus was employed, but the soil layers were uniform- 

 ly 9 cms. thick. The germicides were mixed with the soil in the dry 

 state or in solution at the rate of 25 to 200 mgms. per 60 to 70 gms. of soil 

 (contaning 80 per cent of water). 



Copper sulphate. — Even with the maximum doses of 0.2 gm. CuSO* 

 5H^0 per 12 gms. of dry soil, losses of nitrogen were not completely 

 avoided. With the small doses, denitrification was intensified. This unex- 

 pected behaviour on the part of copper sulphate was probably due to the fact 

 that the greater part of the salt is precipitated as humates in a peaty soil and 

 thus loses its toxicity. The humates which are hardly ionised actually 

 seemed to have a stimulating effect on the denitrifjdng bacteria. 



Magnesium sulphate and zinc sulphate. — Neither of these salts totally 

 inhibited denitrification. With zinc sulphate the action was diminished a 

 little, but with magnesium sulphate it was nearly always slightly increased. 

 Probably with both these salts too the results are due to the formation of 

 non-ionised humates. 



Non-ionisahle substances. — In a last series of experiments, disinfect- 

 ants which did not owe their germicidal properties to ions were used : 

 i. e. carbolineum, toluene and carbon bisiilphide. Where carbon bisul- 

 phide was used the period of incubation was increased from two to five weeks 

 during which time the soil was maintained at ordinary room temperature 

 instead of at 28° C. The following residts were obtained: carboHneum in- 

 creased denitrification; toluene had no stimulating effect in whatever 

 proportion used but neither did it have an inhibitive effect except in one 

 single instance; carbon bisulphide on the other hand always decreased 

 denitrification even when used in very small doses. 



It would therefore appear that on peaty land, carbon bisulphide may 

 be recommended as the best germicide to employ. 



1061 -The Chemical Composition of Plants as a Guide to the Fertility of the Soil. — 



Sawin p. in /7w/j7Hrt./o Onum-HOU Ajpoyo.vin (Review of Agricultural Experiments) 

 Vol. XVjI, Xo. I, pp. 1-12. Petrosrad, 1916. 



Two series of investigations were carried out to determine the rela- 

 tionship between the phosphoric acid content of the plant and that of the 

 soil in which it had been grown. In the first series oats were grown in sand 

 to which nutrient solution was added. Each vessel contained 7 kg. of sand 

 and the nutrient solution was that of Prianichnikoff, i. e. phosphoric acid 

 in the form of Ca HPO* + 2H2O and nitrogen in the form of ammonium ni- 

 trate, both being used in the proportions laid down by Hellriegel. The 

 solution was used at normal streiigth, double strength and treble strength. 

 In the second series of experiments the sand was replaced by two soils, 

 one of which was a poor sandy forest soil from the Agricultural Institute 

 of Moscow and the other a tchernozium (black soil) from the Kharkov 

 Agricultural Station, unresponsive to ])hosphate manuring. Calcium pho- 

 sphate and potassium nitrate were added in quantities equal to normal 

 strength and to 2, 4 and 8 times normal strength. 



When the oat plants were harvested, the grain was separated from the 



