Dec. 1, 1919 Effect of Salts and Organic Extracts on Citrus Seedlings 2 73 



from 1,400 to 2,000 parts per million — that is, it would approach the 

 toxic limit. The surface crusts in citrus groves are often highly toxic to 

 citrus seedlings. 



However, mixed salts in the soil are not as a rule so toxic as the indi- 

 vidual components. The protective or antagonistic action of calcium, 

 for example, when added to toxic solutions of many inorganic salts is well 

 known. Kearney and Cameron * found that gypsum and lime greatly 

 increased the tolerance of white lupine and alfalfa seedlings for most of 

 the salts found in saline soils. Osterhout has observed antagonism in 

 many mixtures of salts and has shown that, in general, if one salt in- 

 creases and the other decreases the permeability of the protoplasm, as 

 determined by electrical conductivity, then the two salts tend to be 

 antagonistic.^ He has also found that while none of the monovalent 

 ions, excepting hydrogen, decrease permeability, all the bivalent ions 

 tested (calcium, magnesium, barium, etc.) do so to a marked degree.^ 

 In other words, the two groups are antagonistic. 



It was consequently to be expected that calcium carbonate would in- 

 crease the tolerance of citrus seedlings for sodium nitrate or potassium 

 nitrate. The effect was most pronoimced with a mixture of sodium nitrate 

 and calcium carbonate (solid phase present) in which a concentration of 

 6,000 parts per million of sodium nitrate, or over three times that with 

 sodium nitrate alone, was reached before the death of the root tip oc- 

 curred (PI. 34, E-G). With ammonium sulphate the death limit in the 

 presence of calcium carbonate was reached at a concentration of about 

 2,000 parts per million, or twice that with ammonium sulphate alone. 

 The filtrate obtained after shaking the higher concentration of sodium 

 nitrate with calcium carbonate in excess and removing the solid phase 

 produced as good plants as when the solid phase was present. The 

 mechanical or adsorptive action of the latter, therefore, has no effect. 

 The addition of small quantities of quartz flour, carbon black, or organic 

 matter to the solution was also without effect on the toxic limit of the 

 nitrate solutions. 



When calcium nitrate or calcium sulphate in concentrations equivalent 

 to the saturation concentration of calcium carbonate in water (10 parts 

 per million) was added to sodium nitrate solutions, the toxic limit was 

 not raised appreciably above that of sodium nitrate alone. As the con- 

 centrations were increased, the protective action developed; and in con- 

 centrations of 100 parts per million calcium chlorid or calcium sulphate 

 was ^bout as effective as calcium carbonate in raising the toxic limit of 

 sodium nitrate. On account of the reaction between sodium nitrate and 



1 Kearney, Thomas H., and Cameron, Frank K. effect xtpon seedling plants op certain compo- 

 nents OF alkali soils. In V. S. Dcpt. Agr. Rpt. 71, p. 7-60. 1902. 



'Osterhout, W. J. V. on the nature op antagonism. In Science, n. s. v. 41, no. 1050, p. 335-256. 

 1914. 



' Osterhout, W. J. V. on the decrease of permeability due to certain bivalent rations. In 

 Bot. Gaz., V. 59, no. 4, p. 317-330, 11 fig. 1915. 



