Interesting . . .
If it was 20 years ago and I needed a beam sticking out of the ground, I'd hire an auger truck like the utility companies use, set the beam upright, and fill the hole with concrete. Done that way, the beam would not need to be that deep and it wouldn't be subject to rusting like steel exposed to wet soil. When I was a lot younger, I set a huge sign for a business. Had a hole dug, put in a re-bar cage with 1 1/4 bolts protruding and poured the hole and supporting base with concrete. When cured for about 10 days, we bolted the sign upright in place and had the big sign mounted.