Geoffrey Burnitt died four days after being trapped by the hydraulic arm of a bailing machine at Stainforth Moor Peat Works in Thorne on March 2, 2006.
Mr Burnitt was found trapped in the bailer after entering the machine through a gate which had a broken lock and activating a sensor which started the machine.
Mr Burnitt (54) from Goole, was found on the floor by the machine by work mates during a shift in the early hours of the morning.
The hydraulic arm of the machine was pressing down on his back and shoulders.
Sheffield Crown Court heard how the door remained broken for four days and had been hastily tied shut with cable ties with a handwritten warning put in place.
Surrey-based Scotts Company (UK) Ltd was fined £80,000 and ordered to pay nearly £20,000 pounds in costs after it admitted failing to ensure the health and safety of an employee.
Judge Graham Robinson said at the very minimum the gate should have been secured by a chain and padlock. He said: "The problem with a handwritten sign is that it is unprofessional, does not demand
attention and loses impact very quickly.
"The Health and Safety legislation is there to protect employees from the consequences of their own momentary lack of attention to detail - even the most experienced employee can overlook or forget an important piece of information."
Alex Offer, prosecuting for the Health and Safety Executive (HSE), said that the gate was usually fitted with an electric locking system.
Workers on duty were spoken to but no mention of the makeshift job of securing the gate was mentioned at shift handover, and no record was made on a message board for the firm's engineers, he added.
In mitigation Mark Bishop said that steps had been taken to ensure such a tragedy would ever happen again.
After the hearing, HSE inspector Richard Noble said: "It is not good enough at any time to rely on temporary or makeshift arrangements in the hope that these will be adequate for safe working."