Hmmm, Grassy. Suppose a cubic foot of leaves weigh 10 pounds, and there would be 27 cubic feet in a cubic yard--therefore weighing 270 pounds, And therefore the pile of 100 cubic yards would weigh 27,000 pounds. I dunno--if it is mostly carbon, and you want a 40 to one ratio, you need 675 pounds of nitrogen. That seems like a lot--maybe someone with more experience or expertise can add more comments. The leaves may have a few percent nitrogen in them to start. There may be some grass clippings in the pile already.