Nitrogen Fixer / Nitrogren Lifter - Green Manures

[mew]

Ok, I know it doesnt take much but im confused

First year at growing so im completely clueless but Ive gleaned that putting a green manure on about now is a good way of fertilizing the soil for next year when it starts all over again.

Just been looking at a website and I notice its going on about nitrogen lifters and fixers - I thought green manures were there to put nitrogen back into the ground replacing what the previous crop has taken?

Do the nitrogen lifting manures hold the nitrogen in the plant itself so its released once its dug back in perhaps?

Apologies for the stupid questions.....

Thanks
MEW

[possum]

nitrogen fixers take nitrogen from the air and either put it into the plant itself (which you then dig in) or over time put it into the soil
tree lucerne is a great nitrogen fixer, our soil is crap. but underneath the lucerne the grass is luxuriant. not a solution for the veggie patch, but great for pasture.