Let's break down what the phrase seems to mean:
* Low: Suggests a feeling of being down, dejected, or depressed.
* Belly: Refers to the lowest part of the body, highlighting a sense of being stuck or unable to move.
* Wagon rut: Wagon ruts are the deep grooves left in the ground by wagon wheels, often muddy and difficult to navigate.
Therefore, the idiom likely conveys a feeling of being extremely low, stuck, and trapped, like a belly sinking deep into the mud of a wagon rut. It signifies a sense of being trapped in a difficult situation with no easy escape.
However, it's important to note that this idiom is not widely recognized. If you heard it used, it might be a specific, localized saying with its own particular meaning.