The fava bean forest got cleared out today to make room for tomatoes. When I pulled up the towering plants I was glad to see that the root clumps are festooned with clusters of nitrogen-fixing nodules. That means that these fava plants, like all hard-working legumes, invoked their magical powers of pulling nitrogen out of the air and storing it in tiny sacs strung along the root systems.
Actually, the whole story is more complicated. The fava roots exude sugars into the soil to attract a particular type of bacteria which attach themselves to the roots. These bacteria are able to convert nitrogen from the air into a form that the plant can use. What the plant can't use right away is stored in the nodules. (I don't really understand this part. How does the nitrogen get to the bacteria way down on the roots?)
Here are the sturdy stalks and root clumps ready for the compost pile. If I were able to leave all this material in the bed and dig it under so it could break down right in place, the nodules would enrich the soil with their stored nitrogen.
Also, if I had dug in the plants before they formed their ample harvest of beans, there would have been lots more stored nitrogen and lots more enrichment. Unfortunately, none of these "ifs" are going to benefit the tomato seedlings which need to go into this bed right away.
But the extra nitrogen won't go to waste and will eventually make its way back to the garden as compost.
Meanwhile, here's a link to a great little video where a couple of enthusiastic agricultural scientists explain nitrogen fixation on soybeans. After listening to these guys, you just can't help rooting for roots! Yay roots!
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