558 Thirty-second Annual Report 



the plot that had always been barren before gypsum treatment. 

 These studies, which extend over a period of years, have been put 

 in manuscript form and crop maps have been prepared for pub- 

 lication. 



INFLUENCE OF CONCOMITANT CONDITIONS OF THE TOXICITY 



OF BLACK ALKALI 



The work has been in progress for several years as an 

 Adams fund project. In the pot culture phases of this in- 

 vestigation interesting and suggestive results have been ob- 

 tained with winter cultures of wheat and barley. Attempts 

 with summer cultures so far have failed almost entirely. In 

 1920, tepary beans and cotton were used, but neither proved of 

 value for pot cultures. This year milo, hegari, and Mexican 

 June com are being used. Corn is doing fairly well, but the 

 first planting of milo and hegari failed to come up or died im- 

 mediately in the same pots where wheat and barley had given 

 fair returns the previous winter. Even in the low concentra- 

 tion, .05 and .075 percent sodium carbonate, these sorghums 

 made very weak growths and were nearly destitute of chloro- 

 phyll. The pots have been replanted with the same sorghums. 

 Milo and hegari have behaved almost the same way on the 

 black alkali plots on the University Farm where barley made a 

 good winter growth. Check pots with sweet soil are giving 

 good growths with both of these sorghums. It is difficult to 

 find a crop suited to summer pot culture work with alkali under 

 the climatic conditions prevailing at Tucson. Rhodes grass, 

 however, on strong black alkali soil at the University Farm is 

 making a fine growth. It may prove of value for pot culture. 



With winter cultures wheat proved much more resistant to 

 black alkali than barley, which is contrary to the generally 

 accepted belief. It may be a matter of variety, however, for 

 the wheat used was Sonora and the barley was ordinary six- 

 row. Six series of cultures were run with both wheat and bar- 

 ley in which the concentration of black alkali was the only 

 factor varied. Barley failed absolutely in .25 percent (by anal- 

 ysis of the natural soil) sodium carbonate, while wheat made 

 a slight growth. Barley made a very weak growth in .20 per- 

 cent sodium carbonate and wheat a fair growth. In weaker 

 alkali both wheat and barley made satisfactory growth for 

 experimental studies on soil of the University Farm type. Very 

 little difference was discernible in the weaker black alkali cul- 

 tures as judged from general appearance, but the grain yields 



