Nitrogen Fixing Root Nodules

Last year we wrote about our Field Bean Experiment.

Inspired by results from Garden Organic, we allowed a section of our Green Manure Field Beans to grow on as an edible alternative to Broad Beans, and also to seed save for replanting this year.

We have been more than happy with the results on all fronts. Gradually eating our way through a winter store of frozen beans, while once again digging in the majority of the winter replanted field beans as green manure this spring, but leaving a portion to grow on to repeat the virtuous cycle.

Eating our way through the winter store of frozen beans

Field Beans are an overwintering green manure that germinate well in colder weather from Sept to Nov, with deep roots that break up the soil and fix nitrogen. The green manure is then cut down and dig in during spring.

But they can be grown on for consumption too, because Field Beans are the same species as Broad Beans, just a different variety producing smaller but more vigorous beans. And as we can attest, just as tasty.

Seed saved for replanting this year

Beans are one of many plants that are well known for doing nitrogen fixation via root nodules which transform environmental nitrogen into nitrogen for the soil, a key nutrient for plants.

Apparently, these amazing root nodules aren’t exactly part of the bean plant. Instead, they are the home for a bacterium that works symbiotically to exchange carbohydrates from the plant for the bacterium for ammonium for the plant from the bacterium.

Between our experimental planting last year, and the start of a new cycle this year, we were able to capture pictures of the field bean roots to show these beneficial nitrogen fixing root nodules at the green manure stage, compared to the bare roots of the mature grown on and harvested plants once the nitrogen had all been used up. Truly a marvel of nature.

Field bean roots with the beneficial nitrogen fixing root nodules at the green manure stage in spring
Bare field bean roots at the mature grown on stage in autumn

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