No Nodules!

My bean plants this year have been pretty disappointing; the yields were smaller than I expected, the leaves were discolored, and they didn't grow nearly as tall as they were supposed to. And, plants that were supposed to last until fall have been slowly dying the last few weeks. Finally, I decided to pull some of them up and replant. And look what I found: no nodules on the roots! Here's what they should look like:
http://www.flickr.com/photos/fluffymuppet/2603848846/

(No, I am not fluffymuppet.)

I've always thought that buying commercial innoculant was a waste of money, as everywhere else I've planted beans they've grown quite happily without it. However, I think maybe the high temperatures of the city compost pile killed off the bacteria that produce the nodules and help the plants fix nitrogen. I pulled up several green beans and almost all of my black beans and found the same thing under all of them.

ETA:
Inoculant is a powdery substance that you can put on your legumes just before planting them. It contains a bacterial culture that infects and works symbiotically with legume plants to "fix" nitrogen from the air. Usually I think there is plenty of this bacteria outside for the bean plants to do well, but apparently not in my new plot. Now I have to do an experiment with some inoculant next year!