Ray Frederick, contracts support officer at Hertfordshire County Council, said mowing verges and grounds for 600 local schools racked up big fuel costs.
He claimed that the rules defined horticulture too narrowly. Tractors used for cropping and harvesting could buy the cheaper red diesel, but not kit used for landscaping and recreation.
Red diesel is about half the price of ordinary diesel and can be used only in vehicles deemed by the Government as "essential" for food production or working on land.
Tractors towing mowers - quicker and more efficient for large-scale cutting - are outlawed from using the diesel, dyed red to help tax inspectors identify lawbreakers.
Frederick said: "A wider definition of horticulture could allow other vehicles to use red diesel.
"Physical education in schools, for example, is not only essential but a statutory requirement. So mowing playing fields should fall into the essential category.
"If you have contractors dealing with hundreds of schools, the difference is tens of thousands of pounds. Companies on fixed contracts have to absorb the cost."
Frederick has written to BALI and the NFU, which have yet to respond.
Tax chiefs told him via email: "Whether there is some educational benefit to the maintenance of facilities such as school playing fields is not the point."
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