Jan. 27, 1919 Influence of Salts on Nitric Nitrogen in Soil i ^^ 



cation to three-fourths normal than is required to produce the same 

 effect upon the nitrifiers. It is evident from these results that the 

 common soil alkalis, calcium chlorid, sodium carbonate, sodium sul- 

 phate, and sodium nitrate, are very toxic to nitrifying organisms, and if 

 present to any great extent, will greatly reduce the nitric-nitrogen con- 

 tent of the soil. 



The toxicity of the compound to ammonification was found to be 

 controlled largely by the cation, but no such a relationship is found to 

 exist in the case of the nitrifiers, as can be seen from figure 5. 



The toxicity of the compounds to ammonification was found to be 

 controlled largely by the cation, but no such relationship is found to 

 exist in the case of the nitrifiers (fig. 5). 



SUMMARY 



The toxicity of the chlorids, nitrates, sulphates, and carbonates of 

 sodium, potassium, calcium, magnesium, manganese, and iron as deter- 

 mined by nitrification is detennined by the specific salt and not by the 

 electro-negative ion, as was the case with the ammonifiers. With the 

 exceptions of the manganous chlorid and sulphate and the chlorids of 

 iron and sodium, the salts tested all became toxic at a lower concentration 

 to the nitrifiers than to the ammonifiers. 



The quantity of a salt which can be applied to a soil without decreasing 

 the nitric-nitrogen accumulation in the soil varies with the salt, and for 

 the soil under investigation it is in the order of decreasing toxicity of the 

 salts as follows : Sodium sulphate, sodium carbonate, calcium carbonate, 

 potassium sulphate, potassium carbonate, ferric nitrate, sodium nitrate, 

 magnesium sulphate, ferric sulphate, calcium nitrate, potassium nitrate, 

 potassium chlorid, magnesium nitrate, manganous carbonate, manganous 

 chlorid, manganous sulphate, ferric carbonate, magnesium chlorid, man- 

 ganous nitrate, ferric chlorid, magnesium carbonate, sodium chlorid, 

 calcium chlorid, and calcium sulphate. 



It is not necessarily those compounds which become toxic in the lowest 

 concentrations which are most toxic in higher concentrations, as the 

 toxicity of some salts increase more rapidly than the toxicity of others. 



It is quite evident from the results reported that the increased osmotic 

 pressure exerted by the salt added to the soil plays a minor part in the 

 retarding of the bacterial activity. The main factor is probably a 

 physiological one due to the action of the substance upon the living 

 protoplasm of the cell, changing its chemical and physical properties so 

 that it can not function normally. 



The common soil "alkalis," calcium chlorid, sodium sulphate, sodium 

 carbonate, and the less common one, calcium nitrate, are very toxic to 

 the nitrifying organisms, and if present in soil to any great extent will 

 greatly reduce the nitric-nitrogen accumulation in such a soil. 



