You can't beat radish (Raphanus sativus) for a quick response to N. 18 days
from seed to harvest (under fluorescent lights)! They are genetically
homogeneous, easy and cheap to obtain, produce a root AND shoot (a recognisable
crop), a simple leaf which can be measured for area by lxbx"a conversion
factor", simple and cheap water culture method etc.
One novel feature is that you can line the roots for each treatment up
side-by-side to produce a "radogram" to simply/visually demonstrate the increase
in root yield up to 112ppm N but a reduction at 224ppm N (photo in the
reference below). Total dry mass reaches a maximum at 112ppm and then levels
off. ca.80% dry mass in shoot at low N reducing to ca.40% at 112ppm and back to
ca.60% at 224ppm.
You will find full details of how to grow radish to demonstrate N response and
full results of such a growth analysis in School Science Review (Sept 1994) Vol
76, No 274 pp45-55.
__________________________________________________________________________
| Dr. John Hewitson |
| Berrystead Barn +44 (0)1832 272 209 phone/fax |
| Oundle, |
| Peterborough, PE8 4DY, UK e-mail 100600.70 at compuserve.com |
|__________________________________________________________________________|
