I can only think of salt! Is yeast a nutrient? Would it work? Thank-you!
Nitrates Phosphates Potassium (so there is your famous NPK trio) magnesium (to prevent leaf yellowing) You would need (for example) an inert culture medium like vermiculite and a series of identical plants (eg cuttings, offsets etc) some you would water with all of the nutrients (in suitably dilute form) but miss out the nutrient you are investigating (e.g. nitrate) and some you would water with all the nutrients including the one you are investigating. By comparing the two groups you could get some idea of what the nutrient was used for. (If you deprive a plant of nitrates it generally remains stunted because the nitrate is needed for protein production which is in turn needed for growth). John
