Help needed!

High all,
I spotted my largest girl who has been flowering for 3 weeks and the bottom large fan leaves are turning yellow, also I spotted a large green root popping out over the soil. Is my plant root bound by any chance?
My plant is just under 6ft and the pot I have is a 3 gallon bucket.
Heres some pics.

yea a bigger pot would be the order of the day see if that stops the leaves yellowing.