This is a really cool idea for lots of reasons, but especially because you could leave sensors buried forever. This lends itself well to long term soil monitoring-- A somewhat unsolved problem especially in no-till environments.

Agriculture is a harsh place for sensitive electronics. My approach has been to make them cheap enough to be nearly disposable (shameless plug, https://github.com/alexose/dorothy), but this still requires a lot of human intervention to keep everything chirping.