waste
埌 centers on waste or barren land, likely referring to a desolate, unused area of earth.
埌 combines 土 (earth) with 良, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with waste or barren ground.
The left side is earth 土, and the right side 良 looks like a pile of discarded things. Picture a mound of waste on the ground.
For ロウ, imagine a low, wasted patch of earth: low -> ロウ, and the ground is barren and unused.