Farm tractors are all diesel.
So you said - any idea why?
Well, let’s be accurate: _Today_ all farm tractors are diesel.
Before 1970, farm tractors were made with diesel, LPG and gasoline engines.
Before about 1950, most all farm tractors used gasoline; some used “distillate” and started on gasoline and switched over to distillate. Of course, back then, lots of farm tractors were started by hand. Starting a gas engine by hand? Unpleasant, but possible. Starting a diesel engine by hand? You’d better be hung like a Clydesdale to pull that thing over TDC.
The reason why farmers went to diesel engines was the higher torque and efficiency of the diesel engine, not the power density of the fuel.
Today, there’s additional issues of fuel taxation that come into it. You can buy diesel fuel that has no road taxes levied on it - it is dyed red.
You cannot buy non-tax gasoline. You can buy road gasoline, keep very close records and apply every quarter for a tax rebate, but I’m here to tell you that it is a pain in the posterior.