50 



TOXIC LIMITS OF ALKALI 



parts per million of this salt. For sodium carbonate the 

 relationship between sand and solution cultures was about 

 1000 and 5000 parts per million, respectively, and for 

 sodium sulphate it was about 5000 to over 10,000 parts 

 per million, respectively, for half-normal crops of dry 

 matter. Le Clerc and Breazeale (17) found wheat seed- 

 lings more tolerant for sodium chloride in sand than in 

 solution. Breazeale (2) states that the reverse relation- 



FIG. 6. EXPERIMENTS TO DETERMINE THE TOXICITY OF 

 VARIOUS ALKALI SALTS. 



ship for nutrient solutions holds, 300 parts per million of 

 nutrient solution being the best concentration for wheat 

 seedlings, while 2500 parts per million was best for them in 

 sand. Others have found the latter relationship to hold 

 for sand. The size of pure quartz sand particles ap- 

 parently had no effect on the toxicity of alkali in tests 

 made by Harris and Pittman (n), but the quantity of 

 moisture in the soil had considerable influence. 



The differences which may be expected in alkali experi- 

 ments with differing moisture contents are shown in tests 



