It is interesting that you bring this up. Zinc is very important to humans as well as trees Zinc - Mayo Clinic . It is very interesting that “Zinc deficiency can declines T cells generation and depresses humoral and cell-mediated immunity” in people with infectious diseases Nutritional status and serum zinc and selenium levels in Iranian HIV infected individuals | BMC Infectious Diseases | Full Text . This thread validates your point Influence of soil nutrients on fruit flavor? . Wait until you see this old apple thread Growing better apples with zinc . Boron and zinc come up numerous times Search results for 'Zinc' - Growing Fruit . @richard and others with fertilizer making experience realize the importance of zinc the same as you do.
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