138 BIOLOGICAL CONDITIONS OF THE SOIL 



of sodium sulphate. For one-half normal ammonifying 

 power, Greaves found the points to be at 11,660 parts 

 per million of sodium carbonate, 1170 parts per million of 

 sodium chloride, and 8520 parts per million of sodium 

 sulphate. The results of Brown and Johnson (3) indicate 

 a lower limit, but all show that sodium chloride is the most 

 toxic. The relationship of the three salts is nearly re- 

 versed to that in their action on plants. Greaves (5) found 

 sodium nitrate to be toxic at about 426 parts per million. 

 He noticed a stimulating effect of sodium carbonate, 

 sodium nitrate, and sodium chloride in decreasing order 

 when only small quantities of these salts were present, 

 but found none with sodium sulphate. x His experiment 

 also showed that some salts increase in toxicity with in- 

 creasing quantities of salts much faster than others. 



Lipman (9) noticed antagonism between the anions of 

 the sodium salts, the action being strongest between 7000 

 parts per million sodium carbonate and 2000 parts per 

 million sodium chloride, next between sodium carbonate 

 and sodium sulphate, and weakest between sodium chlo- 

 ride and sodium sulphate. Antagonism was noted "be- 

 tween toxic and stimulating salts as well as between two 

 toxic salts." A reduction of the stimulating effect of 

 sodium carbonate on ammonification was noticed by 

 Brown and Johnson (3) when calcium carbonate was added 

 to the soil, but the toxic effect was also reduced. Both 

 sodium chloride and sodium sulphate showed more stimu- 

 lation and certain toxic quantities became stimulating 

 when calcium carbonate was added. "Combinations of 

 various salts in non-toxic individual amounts in the pres- 

 ence of calcium carbonate became toxic to ammonification." 



Other soil organisms have been little studied. Hun- 

 ter's (16) experiments show that Actinomycetes were 



