Highlighting the issue this week, the Scottish Environment Protection Agency pointed out that, between the mid-1980s and 2006, AGCO UK – under the Massey Ferguson trade name – supplied around 850 combine harvesters in the UK fitted with crop yield meters containing these radioactive sources.
Specifically, the three combine harvester series involved are the MF 30, the MF 40 and the MF 7200 range, commonly called the Cerea range.
The radioactive parts, while of no significant risk during normal operation, only become an issue if the combine is scrapped, stolen or involved in an accident.
SEPA radioactive substances specialist Isabelle Watson said: "These sources are designed to withstand the rigours of normal use. However, owners do need to be aware that radioactive sources are subject to specific legislative requirements which SEPA and HSE enforce in Scotland.
"Under the Radioactive Substances Act 1993 (RSA93) you must apply to SEPA for a certificate of registration prior to obtaining the source (taking receipt of the combine harvester).
"Once issued, SEPA will periodically inspect you as a holder of a registered source for compliance with the various registration conditions which are intended to ensure the source is kept and used safely.
"When the crop yield meter is no longer required and is to be taken out of service it is essential that the radioactive source is disposed of safely via a specialist waste disposal company."
Ms Watson pointed out that AGCO UK is currently offering a free radioactive source disposal service, but that is set to end on December 31 this year. After then, disposal costs via a specialist contractor, are likely to be of the order of a few thousand pounds and will be the land manager's responsibility.
AGCO will also stop offering its free Radiation Protection Advisor at the same time, again requiring farmers who continue to work with these devices to make arrangements with a competent and suitable RPA – who is likely to charge commercial rates.
Commenting, NFUS policy manager, Andrew Bauer, said: "NFUS would urge farmers with combines in any of the listed classes to check their crop yield meter and consider their options as soon as possible.
"If you are unsure about the meter's sealed source status, please call SEPA's helpline and make sure you're in the clear," he suggested.