A square or rectangular hay baler (10) comprises a fore and aft hay bale forming zone, and a cut vegetation pick up and delivery arrangement for delivering cut vegetation to the hay bale forming zone. A compression plunger (19) of the hay baler (10) is movable in the fore and aft direction for compressing cut vegetation into a bale in the hay bale forming zone. A reservoir (23) retains a supply of non-toxic liquid surfactant or lubricant, and a pump (25) is provided for pumping the nontoxic liquid surfactant or lubricant from the reservoir (23) at a supply pressure to one or more discharge outlets (32) in the hay baler (10). Thereby, inwardly facing surfaces in the fore and aft hay bale forming zone are at least partially coated with the non-toxic liquid surfactant or lubricant.
