Growing in Sand

Hi there,
We are starting a community garden in New Orleans on a sanded over lot.
there is about 40cm of sand on top of clay hardpan, not ideal growing conditions.
the lot is huge! we are planning on sheet mulching the whole thing and have already started bringing in loads of soil, spent grain from breweries, mardboard and anything else that we can get our hands on that will make good soil.
the lot is 50 by 125 feet. bringing in enough matter to cover the whole thing with enough soil to make a decent growing medium is a LOT of work. especially when out budget is all of 0$.
looking for biomass generating, soil conditioning and nitrogen fixing plants that will thrive in sand and grow FAST!
we want to make the space look productive and yet keep it from looking like just another blighted lot....
plant list anyone?

cowpeas, sweet potatoes, okra... all the typically southern-grown veggies should grow fine there once you've mulched.

if you can get mimosa or ear-tree in there, they could be good for shade and chop and drop.

it sounds like you are on the right track. dont overlook raised and sunken beds.

The problem is getting all the OM there in the first place.
it a huge area and we don't have the resources to truck in enough OM ro cover the whole place.
What im looking for, are plants that will grow in the sand that is currently covering the lot.
I think the peas might work but they don't produce a large amount of biomass that i can chop and drop.
need plants that will make LOTS of biomass FAST!
either above (leaves stalks etc) or below ground (Roots).

Sunhemp will produce a huge amount of biomass for you. The seed can be a little pricey...but it's an amazing plant and the seed goes a long way.

This is where I buy from. Lots of other annual legumes and grasses to look at there too.

do you think that sunnhemp would grow in sand?

I'm planting it for the first time here in Florida this summer...i'm on a sandhill. An extension agent told me she had great success with it on sandy soils, so I assume it will.

the absolute easiest and cheapest way to get a lot of biomass fast is to go get either birdseed or dried beans from a well-used big box store like wal-mart. birdseed is much cheaper but does not fix nitrogen like the beans will. all my cowpeas came from the grocery store.
also many municipalities have a free dump site where you can get chipped yard waste, it's where i get all my mulch.
if you know anyone with pets you might be able to get manure for free too. it might take some gross work to get it though

15 inches of sand on top of clay in a wet environment. That's awesome stuff! Like the above poster said, go buy some dried beans you don't hate eating. Plant one every foot or as many as you can afford. You might try alfalfa too. It is either edible or I'm dead, I'm not sure, I haven't checked. Next year try other stuff like Quinoa, Flax, Amaranth, and some kind of squash like plants along with beans.

Thanks Guys!
unfortunately, I have not found any good free mulch sites as of yet in New Orleans...but im sure they will happen! I'm gonna start broadcasting seeds over the whole lot asap. mostly beans and peas and if i can get my hands on some sunnhemp and amarath seed i'll get those down too.
thanks for all the help permies and if you have any other tips or advice, ill gladly take em!
cheers

sweet potatoes don't need a lot of organic matter in the soil, just some periodic irrigation, so you could get growing on something this year. there's a good chance they can overwinter there in new orleans without digging, though i wouldn't try to overwinter the whole crop just in case.