I've just finished reading the book Miracle Apples where Akinori Kimura goes through his decade long struggle to learn many of the things we have handed to us on a silver platter by the likes of Mollison and Holzer. And I
should add Hemenway, Jacke and Toensmeier to that list as their
books let us
skip past a lot of the painful learning process.
Anyway, something Kimura commented on regarding nitrogen fixation was new to me. I don't recall hearing about it in any of the
Permaculture stuff I've read thus far. Kimura uses soybeans for his N-fixing needs (not surprising in Japan) and observed that when he first started doing this he had many many colonies of bacteria on the
roots fixing nitrogen, but over the course of 5 years these diminished to the point of not having any. He observes the nodules on the roots to know when more nitrogen is needed and he plants more or fewer soybeans as required.
Now this rings true because we know that things done naturally will find the right balance. But I've never even considered having 'too much' nitrogen. Always not
enough nitrogen: need N-fixers. I haven't been growing things long enough to observe this trend of bacterial nodules myself (I'm in my 2nd season, so I've been happy to simply recognize the nodules at this point!). So what would happen if there
was too much nitrogen in the soil? Any effect on the plants or visible signs? (read: why would nature limit the amount of nitrogen?) Also, has anyone observed this similar cycle of N-fixing bacteria?