A block heater that goes into one of the freeze plug holes or directly into the block is best but the one I linked you to is a very good option and uses less energy than a true block heater and will transfer the heat better than a magnetic heater as it is siliconed directly to the oil pan.
You might want to go to your local dealer and find out if the engine is equipped for a block heater as it may be and all you would have to do is remove a plug and install the heater.
Say........you didn't get this tractor to farm Marigawanna and be medical care giver did ya?
