This is a pun on 'bail' which is the temporary release of an accused person awaiting trial, sometimes on condition that a sum of money be lodged to guarantee their appearance in court. However, the alternate spelling of 'bale' is used in it's place because it sounds exactly similar and because it is a bundle of paper, hay, cotton, etc., tightly wrapped and bound with cords or hoops.
A hay farmer in jail could get out on bale .