There seems to be a lot of similar and related information on this topic among the many diverse forums at UT, but I thought that I would begin this discussion to gather some of the best ideas that have been mentionned so far to this location. If you think that having this forum is folly because your food comes from supermarkets and not from farms, then this forum is not for you.
Some points for discussion, not necessarily in any order:
1) Small scale terraforming projects such as atrium style dwellings or greenhouses have a certain cost associated with transporting and constructing the building materials.
2) The variety of crops that can be grown successfully to produce large volumes of producce. There are at least a dozen crop plants that grow well in space of which tomatoes are the most promising. Some of the others are common species known as corn, wheat, potatoes, and salad greens. One observation is that the current research may be somewhat one-dimensional because it concentrates on Quaternary atmospheric conditions of the hydroponic mediums. The research could include some experiments in atmospheric conditions different than today. The growing of fern fronds, or else plants that would provide shade or micronutrients to benefit harvestable plants, acting in symbiotic intermediary relationships with one another in atmospheric conditions different than today. Also to be discussed is the ability to withstand radiation exposure: plants growing in regions on Earth of natural radioactivity such as the Great Slave Lake area may shed some useful information for the study of hydroponics in space, or of viable farms on Mars.
3) Machinery, or robots may be of use in maintaning/harvesting the crops.
4) Animal life. On Earth bumble bees are almost 100% employed in greenhouse tomato production. Are they able to fly in zero-G, or low gravity greenhouse environments on Mars? The study of astrobiology may play a role in observing the limits to which bacterial colonies can be manipulated to grow medicines or foods (such as penicillin, mint, etc.).
5) Micronutrients, soil requirements, etc. Can the soil on Mars support life or would it be in need of earthworms and nematodes to assist crop production? What about the dust material found in comets with the unique amino acids found in their soils?
6) Would we recongnize indigenous harvestable lifeforms on other planets if we found them?!
7) Perhaps there are other considerations to be presented on this the topic of "astro-agronomy". Survival of the human race in the space age will depend on continuing efforts to find innovative ways to feed ourselves.