146 INFLUENCE OF SALTS ON THE SOIL 



sodium chlorid, between 0.1 per cent, and 0.2 per cent.; for sodium 

 sulphate, 0.4 per cent.; and for sodium carbonate, 2.0 per cent. A 

 stimulating influence was noted in the case of sodium carbonate, 

 but not in the case of the sulphate or the chlorid. The points at 

 which they became toxic to nitrifiers were found to be: for sodium 

 carbonate, 0.025 per cent.; for sodium sulphate, 0.35 per cent.; 

 and for sodium chlorid, less than 0.1 per cent. 



All except sodium chlorid acted as a stimulant in lower concen- 

 trations. Later Lipman and Sharp found the point at which sodium 

 chlorid became toxic to nitrogen-fixing organisms in soil to be from 

 0.5 to 0.6 per cent.; sodium sulphate, at 1.25 per cent.; and sodium 

 carbonate, at 0.4 to 0.5 per cent. Sodium chlorid was the only one 

 which acted as a stimulant. Recently Lipman has demonstrated 

 that there exists, as measured by ammonification, a true antagonism 

 between sodium chlorid and sodium sulphate; between sodium 

 chlorid and sodium carbonate; and between sodium sulphate and 

 sodium carbonate. 



Brown and Hitchcock found nitrification to be stimulated by 

 small amounts of sodium chlorid, sodium sulphate, and magnesium 

 carbonate, and large amounts of calcium carbonate. The large 

 quantities, however, became toxic, the point at which toxicity and 

 probably stimulation occurs varying with the different soils. 



Variation in Effect Produced. It is quite evident from the liter^a- 

 ture reviewed that the addition of a salt to a soil may produce a 

 number of different effects, depending upon the nature and quantity 

 of the salt added: (1) The salt may stimulate some or all of the 

 bacterial activities of the soil; (2) it may be without effect; (3) it 

 may be toxic to some and without effect or stimulating to others; 

 (4) it may be toxic to all of the bacteria of the soil and hence either 

 kill the organisms or, what is more often the case, materially 

 decrease their metabolic activity. 



These factors are well illustrated in an extensive study carried 

 on by the author on the chlorids, nitrates, sulphates, and carbonates 

 of sodium, potassium, calcium, magnesium, manganese, and iron. 

 They are especially interesting in that it indicates the influence of 

 these twenty-four salts on the ammonifying and nitrifying powers of 

 a soil all tested under similar conditions. Though the results are 

 not absolute, they do represent rather nearly the relative action of 

 the various salts, as may be seen by comparing them with the 

 results reported by others. One fact, however, which the student 

 must bear in mind with these, as with all other results, is that an 

 accumulation of a specific substance within the soil may represent 

 either an acceleration of the activity of the organisms which form 

 that compound or a decrease of the efficiency of the organism which 

 Destroys it, 



