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In page Honey locust:

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The ability of Gleditsia to fix nitrogen is disputed. Many scientific sources[1][2][3] state that Gleditsia does not fix nitrogen. Some support this statement with the fact that Gleditsia does not form root nodules with symbiotic bacteria, the assumption being that without nodulation, no nitrogen fixation can occur. In contrast, many popular sources, permaculture publications in particular, claim that Gleditsia does fix nitrogen but by some other mechanism.[citation needed]