Western Fertilizer Handbook
Ain't got that book. But I didn't see Cobalt in your list. Didnt see Vanadium either. I'm going guess the answer is Cobalt because it is essential in nitrogen fixation. While concentrations in plants vary from .02 to 05 ppm some guys say it's inclusion as a essential nutrient is debatable, is that just a smidg. Now if ya want to debate let's talk about Vanadium. Does anything higher than Algae need it? By the way since B-12 is essential in folks, and cobalt is something ya just gotta have for B-12, does that suggest yet another link some guy needs to explore? Do I get my nickle? Hope so, I want that book.