Help on tomato nutrition demonstration

[Bill Williams]

For several years we've been using a standard tomato nutrition demo
in our introductory biology lab.  We grow tomato plants in hydroponic
solutions deficient in different nutrients and ask students to look at
the plants and use a key to determine which nutrient is missing.

It has never worked well.  Usually, we get very large death rates
independent of nutrient treatment. Typical symptoms begin with
blackening and thickening of the roots, necrosis of above-"ground"
tissue, senescence, and death.
 
Can anyone suggest what might be going wrong?  We've tried bubbling
the solutions with air, but that doesn't seem to make any difference.
 
Some other questions about this procedure:
 	How important is aeration? It's a real pain, and we'd be able to do
many
 	more replicates if we didn't have to bubble air.
 	What's the best way to start the tomatoes, and when should they be
moved
 	to the hydroponic treatments?  Currently we're starting them on
filter
 	paper with distilled water and moving them at the two-leaf stage.
 	
We would greatly appreciate any suggestions!
___________________________________
William E. Williams, bwilliam at oyster.smcm.edu
Divison of Natural Sciences and Mathematics
St. Mary's College of Maryland
St. Mary's City, MD 20686