Check for a label at the pump. It should indicate the sulfur content. We still can't get a straight answer around here. Even the distributors don't know what the refineries are (really) sending them, although it's all labeled ULSD. If your new tractor has DPF, I'd not use a fuel without knowing for sure, even if that means paying road tax. If the tractor has no after-treatment, I might be inclined to just whistle past the graveyard. Only curious, but what is its labeling or rating for biodiesel?