My DIY Soybean Inoculant experiment was designed to create my own inoculant, to save having to order fresh commercial soybean inoculant each year. I described my reasons for conducting the experiment in my last post, Soybean Inoculant Experiment First Results.
DIY Soybean Inoculant Method
To create the inoculant I took an existing method for producing mycorrhizal fungi, and modified it for soybeans. I planted inoculated soybeans into pots and left them to produce seed. I saved the seed to replant, and left the plant roots in the pots to die. When the plants die, the soybean specific rhizobia should remain in the pot soil. By using some of this soil to add to the next batch of soybean plants, I hoped to inoculate the new plants in modules, and repeat the cycle. Some of the soybeans were to be planted out directly into the growing beds, where they would introduce the soy rhizobia to my garden soil. Once all of the beds have grown inoculated soybeans, I will be able to stop the DIY soybean Inoculant experiment, as long as the experiment was successful.
DIY Soybean Inoculant Results
If you take a close look at the plant roots above you shoud be able to see little light coloured balls. These are the rhizobia growing in conjunction with the roots. The picture below shows a close up of a cluster these balls.
The experiment has been a success. This row of four soybeans was the first to be checked. Every plant showed signs of root colonisation, although there were some plants with a very small number of ‘balls’ visible.
Continued Soybean Inoculant Production
Since starting the experiment I have learnt that the rhizobia do not cope well with dry conditions, and I deliberately left the pots to dry out. I may try two versions next year a wet and dry, to see if there is any significant difference. Thinking the process through I also think that I will get better colonisation by restricting plant nutrients, particularly Nitrogen. If the plant is short of Nitrogen it should actively encourage rhizobial colonisation, whereas my habitual addition of compost tea to the daily watering of the modules may have inhibited that. Again that’s a possible experiment waiting for the right time.
Now that I have an ongoing supply of DIY Soybean Inoculant and soybean seed, I can be a little bit more cavalier with the plants. I am thinking that a really low octane potting mix, coupled with regular pruning of the soy plants, may actually produce more rhizobia in each pot. It feels ‘wrong’ to mistreat a plant like that, but it may be worth trying, although measuring how successful it is in producing DIY soybean inoculant would be difficult.
Looking Further ahead this article ‘Natural Nitrogen-fixing Bacteria‘ suggests that over time the rhizobia will co evolve with the native rhizobia in my soil to produce a site specific type that will be better for my plants. How cool is that