Backyard Aquaponics
A place to discuss aquaponics

I was thing of growing soybeans in my aquaponics growing area, although soybeans are a type of legume. Because legumes are used to pump nitrogen into the soil, I was wondering if they would not work as well in an aquaponics setup as opposed to a regular plant?

This is just a guess, but I don't believe legumes release any nitrogen back to the soil until they die. If you pull them from the growbed before they go brown, then it should not be a problem.

Hi Delilah,
We have had good crops of a few different beans and peas in ours. I can't see why soybeans wouldn't work.

Cheers Axl

Legumes work just fine...

Hi Delilah,

Three links to discussions on this topic can be accessed via a thread titled:

Post subject: nitrogen fixation

the url for which is:

viewtopic.php?f=1&t=1826&p=68137&hilit=legume+nitrate#p68137

In particular see the third post from Jaymie which has links to 2 other threads on the same subject.

Those discussions were from 2007 so there may be others since then, so more queries using the forum's search tool will probably find more information.

Somewhere on this forum there was an APer who was short on nitrates and who grew legumes to boost the nitrate levels (reportedly with some success). Once the plant had finished cropping s/he used to clip the top off and leave the roots in the growbed.

If you were using legumes as a classic nitrogen-boosting cover crop (as they do in dirt gardens and farms) then you would clip the top off the plant off before it set seed because the plant transfers a lot of the nitrogren from the roots to the seed at that time.

If you did decide to leave large quantities of legume root material in the growbed you would need to be sure that your growbeds could handle it. Three questions come to mind:

Are your growbeds already overloaded with other dead plant roots and/or solids from the fish tanks?
Is the growbed freely draining and therefore well oxygenated?
Do you have a thriving population of composting worms in your growbeds?

If you have oxygen, healthy composting worms, and no sign of smelly/anearobic rotting zones in your growbeds, then I would expect that your worms will rapidly eat left over legume roots and this would enable the system's nitrifying bacteria to rapidly mineralize the nitrogen-containing molecules in those roots to nitrate (for uptake by other plants).

Good luck.

One aspect I'm still unsure of is whether the bacteria are there in growbeds to do the nitrogen fixing on the plant nodules.

Hello EB,

Where legumes have done well in AP systems, I wonder if they have formed the root nodules?

I read a paper on inoculation of legumes years ago that stated that if a legume is growing well but not developing nodules then it is running off soil nitrogen and could benefit from inocolation with appropriate legume bacteria; at the time these were thought to be all Rhizobia spp. Apparently some soils are deficient in legume bacteria and so the same might easily hold for AP growbeds.

Maybe you'd be better to transplant seedlings into the bed rather than seeds?--if you need the nitrogen.

Peas and beans have been real winners in my systems, growing rampant and with two girls that dont eat greens the wife and I couldnt eat them all. Wont sow so many in the future.

Neptunia oleracea is an Asian aquatic vegetable
It fixes nitrogen
Common English name of water mimosa
I've seen it in systems and it's continually shedding tiny leaflets

Given they are tender enough to use as a veggie, a herbivorous fish or crustacean should have no dramas.

I certainly intend to use it in a catfish setup

In Australia it grows wild in se qld, but you can't cultivate it
There's a native species in western qld neptunia amplexicaula
It's a selenium bioaccumulator
No good for horses who eat too much
But it's edibility for humans would be worth examining

http://en.m.wikipedia.org/wiki/Neptunia ... #section_2

Basic info
Google the rest

Tastes good in a steamboat
Like broccoli / asparagus