How do you use green manure cover crops?

[HonoluluGirl]

I sometimes grow soybeans, and I read somewhere that it fixes nitrogen in the soil and it's also a cover crop. After the beans are harvested, I usually cut the plants down and put them in the compost pile. If I just till them into the soil, how long will it take for the bed to be ready to plant again? I live in Hawaii, so there's really no "winter", and I can plant stuff all year long so I really don't want to have to wait. If I have to wait, then I'll just keep doing what I normally do and put the plants in the compost pile.

Also what exactly does nitrogen fixing mean? Thanks!

[rainbowgardener]

Nitrogen fixing means that it can grab nitrogen out of the air, which it then incorporates into it's tissues as compounds that plants can use. Then when the plant breaks down the nitrogen which was originally in the air is now in the soil.

I think most of the nitrogen ends up in the roots. So if you just cut the plant off at ground level and leave the roots in the soil to break down (compost the plant), you will have captured most of the nitrogen.

[PunkRotten]

So the nitrogen put into the soil is only once the plant dies?

[SOB]

At the base of a bean plant (or any legume) and slightly under the soil the roots create nodules that look like little balls attached to the root stem. These balls contain the nitrogen that has been "pulled" out of the air. When these are kept in the ground to break down they act like fertilizer that has been added to the garden and tilled in. Once the plant is dead these nodules start releasing the nitrogen.

This is a link to a picture of fava bean nodules...
[url]https://summertomato.com/wp-content/uploads/2010/06/fava-bean-root-nodules.jpg[/url]

EDIT: If time is of the essence and you want to re-plant soon I would do what rainbow suggested and cut the plant at the base and compost. Here where we have all winter and early spring for the plant to break down I would till them under the soil and let the entire plant break down.

[HonoluluGirl]

Wow that's cool. I'll have a peek at my roots next time.

[!potatoes!]

So the nitrogen put into the soil is only once the plant dies?

with many nitrogen-fixers, there's a pretty small effect while they're growing, and a big bump of effect when the plant dies or is whacked back. there may be exceptions.

[PunkRotten]

I see. When looking at companion planting they say keep legumes away from root crops. Makes sense, but the fact that it barely adds nitrogen to the soil while it is growing makes no sense to keep them separated unless you actually hack the legume. This whole time I thought the beans growing near my Basil were helping it out.