I'll chime in a little bit here, as my turf discussion class has been working at this subject for the past 2 months. Specifically, we are trying to come up with a plan for a carbon neutral golf course, which has been rather difficult to come by.
At first, the numbers we had led us to believe that a combination of mowing, irrigation, and fertilizing was the culprit, with mowing having the largest impact. Since I love a lot of short grass, this had me worried.
We came upon some new papers and numbers and found that it was actually pesticides that had the most impact, and nothing else was even close. This made me happier, for I believe this to be one thing that can be easily cut down. The reason the numbers for pesticides are so high is that we are looking at embodied energy as well--production, shipping, etc. Embodied energy is really what sets golf courses back from a carbon perspective.
Now, our final set of numbers has fertilizers as having the largest carbon footprint because of energy in production and amounts applied.
Overall, the best thing one can do to make a course more carbon neutral is to have less maintained playing area, sadly. We figure that when looking at sequestration rates, about 200 acres of trees are needed to offset the carbon loss of about 100 acres of maintained turf. That ain't good.
As you can tell though, our process took some dramatic turns with just the discovery of different numbers. This whole things is pretty complex and cloudy right now, and there really isn't anyone else looking too much into it at this point, which is why numbers are so varied and hard to come by. While we may not have it exactly, I can comfortably say that cutting maintained turf is one sure way of reducing the carbon footprint, and reducing fertilizer and pesticide input will help as well. Kind of a lot of work to get to a conclusion that is so obvious.