Wednesday, 21 November 2012

A nitrogen fixation

So I haven't done much today, a) because when it rains like it did today my left knee turns into a brick, and b) because I'm thoroughly hungover.  November 20th will do that at the best of times, but this year was doubly fubar because someone there actually got spat on.

Anywho, I've gone and checked my V. faba for nitrogen fixing.  This can be done quite readily, but may mean the loss of a plant.  Nitrogen fixation doesn't happen because the plant just feels like doing it.  It happens because of a symbiotic infection in the roots by a bacterium called Rhizobium.  Rhizobium causes nodules to form on the roots.  These nodules contain ammonium (NH4+, better expressed as H3N:H+), and when the plant is dug over at the end of its life those nodules decompose, releasing the ammonium into the soil.  Were it not for this process the soil couldn't support the intensity of plantlife that it does, which in turn means the Earth couldn't support anything like the 7 billion humans that are currently walking around.  Chances are that you are alive today because of Rhizobium.  Let's give it a round of applause, shall we?

Rows and rows of Vicia faba
These are too clustered.  Digging up one might hurt the roots of those around it.  Avoid them.  
These are more sparse, so it is far easier to isolate a single plant.  

Using a hand fork, dig out the entire clod that surrounds the roots.  
Use a slow-running tap to gently sluice off the soil.
Examination of the major roots should reveal nodules.

 Alas, I found no nodules.  No nitrogen fixation for me.  The problem might be any one of four things:

  1. I have no Rhizobium in my soil.
  2. I have the wrong strain of Rhizobium in my soil for V. faba.  
  3. My soil is deficient in cobalt, which is a catalyst for the reaction.
  4. These beans are not yet mature enough to be showing nodules.  
I'll give it until this time next month and then I'll lift another plant.

In other news, I'm fairly certain the big Maple is attracting birds...
That is definitely a nest!
...and the Rubus Experiments are a go!

Until next time xx

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