Aug. 28, 1916 Effect on Plant Growth of Sodium Salts 869 



COMPARATIVE TOXICITY OF THE SODIUM SALTS 



In view of the fact that the carbonate and bicarbonate of sodium 

 appear to be interchangeable in the soil, the comparisons of toxicity may 

 be made between the total carbonate salts as previously defined and 

 sodium chlorid and sodium sulphate. Assuming that a reduction of 

 growth of approximately 50 per cent of the check is a critical point of 

 toxicity at which comparisons can be made, it is found that this point 

 is reached with 0.04 per cent of total carbonate salts, with 0.16 per cent 

 of sodium chlorid, and 0.35 per cent of sodium sulphate, using the quan- 

 tities of salt recoverable from the soil — that is, the carbonate salts are 

 four times as toxic as the chlorids and eight times as toxic as the 

 sulphates. 



If the limit of tolerance for the wheat seedling is taken as the point of 

 concentration when both growth and germination are prevented, this is 

 found to be with the carbonate 0.13 per cent, with sodium chlorid 0.52 

 per cent, and with sodium sulphate 0.56 per cent. It is not clear why 

 there is so little difference in these experiments between the limit of tol- 

 erance for sodium chlorid and sodium sulphate. 



SUMMARY 



(1) In reclaiming a tract of salt land in Nevada laboratory experi- 

 ments were carried on to determine the limits of tolerance of certain 

 crop plants to the common salts of sodium. 



(2) These laboratory experiments brought out the fact that only a 

 part of the salt added to the soil in pot cultures could later be recovered 

 from it by water digestion. 



(3) This apparent loss of salt, which was probably due to absorption 

 by the soil, was greater in the case of sodium carbonate and sodium 

 sulphate than with sodium chlorid. 



(4) Where sodium carbonate was added to a soil the absorption was 

 greater in fine soil, rich in organic matter, than in sand. 



(5) The limit of tolerance of crop plants to the salt in the soil is deter- 

 mined by the quantity of salt that can be recovered from the soil rather 

 than by the quantity added to the soil. 



(6) The carbonates and bicarbonates of sodium are mutually inter- 

 changeable in the soil and the toxicity of the soil solution appears to 

 depend upon the quantity of the basic radical held in the soil regardless 

 of the form of the acid radical. 



(7) In the case of the soil from the field under consideration, the pro- 

 portion of recoverable salt which would reduce by one-half the growth 

 of wheat seedlings was for the carbonates 0.04 per cent of the dry weight 

 of the soil, for the chlorids 0.16 per cent, and for the sulphates 0.35 per 

 cent. 



(8) The proportion of recoverable salt which prevented germination of 

 wheat was for the carbonates 0.13 per cent, for the chlorids 0.52 per cent, 

 and for the sulphates 0.56 per cent. 



