David Hershey's reply is right that there are some specific situations
where foliar feeding has been found to have value. I want mention one
aspect that may provide a distraction to your student. Foliar feeding
is often promoted as a miracle cure for all sorts of things. Some of
these work roughly as well as soil fertilization but are are very
expensive; others are pixie dust. If you search the web you are sure to
find plenty of hits in both of these categories.
Zoger Abigail wrote:
> I have a student who is interested in the research on foliar feeding. Does
> anyone have a suggestion of a good review article concerning the effects of
> foliar feeding on nutrients up take as well as pest control? Can plants
> really take up nutrients this way? Or are the plants absorbing the nutrients
> that fall onto the soil from the leaf surface and spraying?