Jan. 27. 1919 Influence of Salts on Nitric Nitrogen in Soil 115 



fying powers of the soil have been reduced to 59 per cent of normal, thus 

 indicating that it is possible to add sufficient limestone to a soil to reduce 

 its nitric-nitrogen content. Whether this be due to its direct action 

 upon the bacterial activities or to changing of the calcium : magnesium- 

 carbonate ratio of the soil can not be answered by these results. It is 

 certain it can not be due to the anions alone, for we find the other calcium 

 salts acting as stimulants. 



Calcium nitrate stimulates only slightly, and this at the medium con- 

 centrations. At low concentrations it is not as toxic as is calcium car- 

 bonate, but at concentrations of 397.1 p. p. m. and above of calcium in 

 the form of calcium nitrate it is highly toxic. At the highest concen- 

 tration tested, 1,191.4 p. p. m., the nitric nitrogen rapidly disappeared 

 from the soil. 



Calcium sulphate stimulated in all of the concentrations tested, and 

 in most cases there was a very marked increase in the nitric nitrogen 

 of the soil. This undoubtedly accounts for the increased plant growth 

 noted when gypsum is added to a soil. When 794.2 p. p. m. of calcium 

 in the form of the sulphate had been added to the soil, there was nearly 

 twice as much nitric nitrogen in the treated soil as there was in the 

 untreated soil. 



Calcium chlorid is apparently toxic at the lower concentrations, but 

 at the higher concentrations it becomes a marked soil stimulant. Its 

 highest stimulation is noted at a concentration slightly lower than that 

 of calcium sulphate. Furthermore, it becomes toxic again, a condition 

 which has not been observed for the sulphate. 



It may be noted that 3 X io~^ mole of calcium nitrate reduces the 

 nitric-nitrogen content of the soil 120 per cent below normal, while an 

 equivalent quantity of the carbonate reduces it 59.1 per cent below nor- 

 mal. The chlorid at this concentration is without effect, whereas the sul- 

 phate is a very strong stimulant. 



INFLUENCE OF MAGNESIUM SALTS 



The compounds used in the magnesium series were the chlorid, sulphate, 

 nitrate, and carbonate of magnesium. The last-named was appUed to 

 the soil in the form of a dry powder, whereas all of the others were added 

 in the usual manner. The results representing the average of four or 

 more closely agreeing determinations are given in Table VII. 



Both the nitrate and carbonate of magnesium increase the nitric- 

 nitrogen content of the soil. In the case of the carbonate this is very 

 marked and is markedly different from the results obtained with calcium 

 carbonate. 



The nitrate, after reaching its highest stimulating point, rapidly be- 

 comes toxic, so that by the time 729.6 p. p. m. of magnesium in the 

 form of the nitrate had been added to the soil, there was a loss of 354.7 

 per cent of the nitrogen. 

 92804°— 19 2 



