Sadly, Anarion is correct.
Besides that, we really don't need to do 3D farming yet. We already produce enough food. World Hunger currently isn't about how much food we produce, but we've already danced that line of politics.
If it were a matter of improving efficiency and lowering the cost of food production, throwing greenhouses over existing farmland would do far more for us, and can easily allow for year round production as per other projects such as www.growingpower.org
Such modifications are probably a better use of our time and materials until the need for 3D farming presents itself. We wouldn't be taking up any additional farmland and we would greatly enhance production and efficiency.