I am working on a class project following nitrogen fixation and this thread has had more useful information than anything I have found to date. Thank you all for your input in the past. Hopefully this is still accessible to you all.
We are testing hypotheses, so we don't need to be right but we need to make good, testable guesses about how nitrogen and nitrogen fixers might be moving around in plants. The underlying goal is to transfer the maximum amount of nitrogen possible into our tree targets.
I have past student projects that found "pools" of fixed nitrogen (N15 depleted) around sweet clover and lupine. Currently we have a cover crop of hairy vetch and winter rye. We are still working toward the experimental design, but we want to test various ways to transfer rhizobium (and nitrogen) in a garden plot.
It's mid March and the vetch has nodules but is not activated. I have found patches of activated vetch on the school grounds. I have permission to move the soils and the vetch for experiments.
I think we are going to plant small (very small) trees in the plot so we can follow them for a year or two (the point right now is to understand nitrogen fixation, not to grow a crop). I think we have time to put down inoculated vetch. We can also move soil from the area where we have activated vetch. I can also move the wild, activated vetch.
The kicker is that we can trace the movement of N by measuring the level of depletion in N15 in plant tissues. For a couple of hundred dollars we can map the whole process with replicated experiments. We have a small budget so that is possible.
Since they are long lived we can follow the trees for over a year. New growth will contain recent sources of nitrogen.
So...where are we likely to mess this up? What hypotheses would you absolutely test? Where are you curious and what would you warn us away from?
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