As the previous posters have said, a black puff of smoke at start-up is normal. Back into your garage so the puff blows out the door.
Use the glow plugs when the temps drop and/or you have to crank several engine revolutions for the tractor to start. My manual has increasing times to operate the glow plug as temps drop. A white puff (or more likely, white smoke for a little while) will occur when the temperatures drop to near freezing. The white smoke (unburned Diesel fuel) will go away as the engine warms up.