126 



Journal of Agricultural Research 



Vol. XVI, No. 4 



INFlvUENCE OF CARBONATRS 



The compounds used in this series were the carbonates of sodium, 

 potassium, calcium, magnesium, manganese, and iron. The results as 

 percentages of nitric nitrogen, the untreated soil being considered as loo 

 per cent, are given in Table XV. 



Table XV. — Percentage of nitric nitrogen formed in lOO gm. of soil containing 2 gm. 

 of dried blood and varying amounts and forms of carbonates 



[The untreated soil is taken as loo per cent] 



Neither sodium nor potassium carbonate stimulate in any of the con- 

 centrations tested, and in this respect they differ sharply from their 

 action on the ammonifiers. Both compounds become toxic at a con- 

 centration of 156X io~^ mole, but the toxicity of the potassium salt in- 

 creases much more rapidly than the toxicit}^ of the sodium salt. The 

 latter, at a concentration of 3X10"^ mole, reduces the nitric-nitrogen 

 content of the soil to 58.8, while the former, at the same concentration, 

 reduces it to 14.8 per cent. 



Calcium carbonate gradually increases in toxicity from the lower to 

 the higher concentrations, whereas the magnesium carbonate, up to a 

 concentration of i X io~^ mole, is a strong stimulant. Although the 

 calcium is toxic at the lowest concentration, and although magnesium 

 stimulates, yet at the highest concentration tests, 3X io~^ mole, there is 

 considerable more nitric nitrogen in the calcium-carbonate- treated soil 

 than in the magnesium-carbonate-treated soil. 



Manganese stimulates slightly when 125X 10"^ mole are added to the 

 soil, above which it becomes slightly toxic, next to iron carbonate; 

 manganese carbonate is the least toxic of the carbonates tested. Iron 

 carbonate is the most powerful of the stimulants tested and becomes 

 toxic only in two concentrations, 625X10"^ mole and 125X10"^ mole. 

 Above and below these concentrations it is a stimulant. 



