Any given year congress could pass something letting farmland owned before X date be passed to your children without taxes. I've seen lots of congressmen telling sob stories about a constituent losing the 8-figure family farm due to taxes. Gates owns the farmland personally, not in the foundation. But it could just be diversifying assets. Lots of tech billionaires buy up lots of land.

He’s donated something like $100 billion already… there’s no chance he’s buying farmland as an inheritance tax dodge.