Habitat is the Key! Food plots are an important quail habitat management tool. They provide emergency winter food that stays above the snow for those winters like we just experienced. Most importantly they provide guaranteed brood-rearing cover.
Many times deer will clean out a food plot by mid-winter and they become useless to quail and other songbirds when snow blankets the landscape. However, you can make your food plot fairly deer-proof by planting the right mixture. My favorite is some kind of taller forage sorghum or sudan grass. The seedheads on these plants grow taller than the deer can reach and then gradually through the fall and winter the seedheads fall over to provide food on and near the ground. Another good deer-proof food plot mix would be german or foxtail millet and pearl millet. Deer do not seem to bother these, but they are a favorite of birds of any kind. You can check with your local agri-service center to see if they have these types of seed on hand or will order them for you.
Most people plant their plots way, too thick. I try to limit the amount of seed I put on by measuring out enough seed to fill a 3-pound coffee can and apply that on every half acre of food plot. A 50-pound bag of 18-18-18 or 12-12-12 fertilizer per acre is all that is needed. You are trying to provide feed for wildlife, not 100 bushel per acre grain crops.