A magazine called The Economist should understand why we use almost all of our arable land for farming. It's because that's the cheapest way to do it.

We could grow all of our food in greenhouses and return 99.9% of our farmland to nature. We don't do that because that would be more expensive and cheaper alternatives make growing wheat & corn in greenhouses highly unprofitable.

Conversely, if suddenly 75% of the arable land came onto the market, it would drive the price of land down dramatically, making it profitable to farm it less intensively (aka more cheaply). In other words, we'd still farm about the same amount of land, but we'd use less fertilizer and herbicide and the price of food would go down. Those are awesome results, but land usage would not be significantly different.