For 10,000 years agriculture has thrived on methods that involve as-is, in-ground growing. The reason that it has been done that way is because it is simple, affordable, and consistently reliable...
I did some math... The huge green-waste recycling center that the largest city in my county operates has an inventory of about 20,000 cubic yards of compost and sewage waste... If that compost was spread out four inches deep it would only cover 16 acres. That is less than 1/3000th of the arable land in my county. I believe that their inventory is severely contaminated by poisons, toxins, and metals that arrive in the yard-waste and sewer system. I would never give that kind of product to someone that I was professing to help.
Presuming that the compost was moved an average of 7 miles to be placed in gardens, and that it was moved in huge loads by dump-truck it would cost around $30,000 for fuel and $50,000 to pay a driver, or $5000 per acre.
Virtually free is not the same as free. The market price of compost around here is around $25 per cubic yard so that works out to $31,000 per acre. If a project started buying up mountains of compost it would make prices soar.
Raised beds are very pricey when constructed from new materials... There would be about 500 raised beds per acre if boxes were constructed at 10 feet by 4 feet. If made a single layer deep from 2X6 boards the cost would be around $35 per box or $18,000 per acre.
The yield of sweet corn is approximately $6000 per acre.
So we have spent more than $54,000 per acre to harvest $6000 worth of food.
There is a very good reason why agriculture has thrived by growing in dirt. It is cheap, dirt is available everywhere without transportation, and it is reliable. The reason that communities have not developed alternatives to growing in soil is because there is no alternative... Sure a few rich people here and there can grow in other mediums, but you cannot feed a civilization by other means. There is simply not enough compost or money.
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