Diesel engine experts at TractorData.com write on tractor fuel types:
Diesel Fuel Diesel fuel first started appearing in large agricultural crawlers in the 1930s, but it was not until the 1950s that diesel became a major fuel source for farm tractors. Difficult starting limited the use of early diesel engines. Some manufacturers built spark-ignition diesel engines, or engines that started on gasoline and were switched over to diesel. Others used small gasoline “pony motors” to warm and start the diesel main engine.
By 1960, diesel engines had greatly improved and were becoming very popular for large farm tractors. By the 1970s, nearly all farm tractors used diesel engines.
LP Gas Liquified propane, or LP, gas was commonly used in the 1950s and 1960s as fuel for farm tractors. Farmers began converting their gasoline engines to LP gas in the 1950s to take advantage of the low cost. Manufacturers soon began offering these engines as an option. LP gas eengines were discontinued as diesel engines began the primary fuel for farm tractors.