Basically the mulching attachment is a big plastic piece that bolts up from the bottom of the deck on the 48". In my area most people do not care for them. They may work better if your grass is consistently dry when you mow however. I've installed Gator blades on the 48" for others and they are generally well received. The theory with those is that they can cut the clippings finer.

Thank Tom Plum. I cut the grass yesterday morning. It had hardly grown since last Sunday and it was totally dry. Even with these conditions the JD threw so much clipping that I had to go over it with a walking mowing to get up some of the clippings. Doesn't seem like a very good design...