Non-essential but useful nutrients for plants would include

Solution (By Examveda Team)

Vanadium and Sodium are non-essential but useful nutrients for plants. Plants require 17 essential nutrients for their growth and development, but vanadium and sodium are not on that list. Vanadium is a multivalent redox-sensitive metal, low levels of vanadium elevate plant height, root length, and biomass production due to enhanced chlorophyll biosynthesis, seed germination and also for essential element uptake.
Sodium is needed by a few varieties of plants to help concentrate carbon dioxide, but in trace amounts to promote metabolism.