So im trying to dig up some data on the subject and i found this ,,,,,,,,,,,,,,,,,,,,,,,,,,,,Dr. H.B. Tukey, renowned plant researcher and head of the Michigan State University (MSU) Department of Horticulture in the 1950s, working with research colleague S.H. Wittwer at MSU, first proved conclusively that foliar feeding of plant nutrients really works. Researching possible peaceful uses of atomic energy in agriculture, they used radioactive phosphorus and radiopotassium to spray plants, then measured with a Geiger counter the absorption, movement, and utilization of these and other nutrients within plants. They found plant nutrients moved at the rate of about one foot per hour to all parts of the plants."
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Foliar feeding is considered especially useful for introducing trace elements, or for "emergency" feeding of plants which are found to have a specific shortage. But in some cases, with tomatoes, for example, it is believed that foliar feeding during flower set causes a dramatic increase in fruit production.
reminds me of that simpsons epiosde with the tamaco