Hi Daniel,
If you're looking to meet caloric needs from a garden, then perhaps grains are the way to go. I'm assuming that you're talking about annual garden crops and not long-term perennials such as nut trees. Let's look at some data that I've pulled from John Jeavons'
How To Grow More Vegetables:
Dry Corn (seed only - cob removed)
Average U.S. yield per 100 square feet: 18.2 lbs
Average protein per lb: 40.4 grams
Calories per lb: 1,656
Wheat, red winter
Average U.S. yield per 100 square feet: 6.4 lbs
Average protein per lb: 55.8 grams
Calories per lb: 1,483
Irish Potatoes
Average U.S. yield per 100 square feet: 84.2 lbs
Average protein per lb: 7.7 grams
Calories per lb: 349
Winter Squash
Average U.S. yield per 100 square feet: 100 lbs
Average protein per lb: 5.2 grams
Calories per lb: 152
OK, let's normalize the protein and calorie data per 100 square feet of each crop for a direct comparison:
Dry Corn: 735 g. protein, 30,139 cal
Wheat: 357 g. protein, 9,491 cal
Potatoes: 648 g. protein, 29,389 cal
Squash: 520 g. protein, 15,200 cal
So, grain corn and potatoes are both efficient crops to produce large amounts of protein and calories. But let's consider other factors. You mentioned that you want to grow drought tolerant crops. Arguably, corn is more of a drought tolerant plant, especially if you grow the flour corn varieties developed by the indigenous peoples in the American Southwest. If we look at the two crops from
permaculture perspective, both are annuals but I think corn can be grown with far less damage to the soil. Common potato growing techniques require trenching, furrowing, and eventual excavation to retrieve the tubers. Corn can be no-till seeded directly into a killed cover crop (winter killed or crimped), can be undersown with a low-growing cover crop such as clover during the growing season, and the dried stalks can be left in place over the winter to provide cover for birds and prevent soil erosion. Plus, corn produces copious amounts of lignified
carbon that is a wonderful addition to the
compost heap. From a storage perspective, dried corn can be kept for years in just about any dry environment free of rodents, whereas potatoes require cold and damp conditions (i.e. a root cellar) and can at best be stored for 6 months. Squash (including pumpkins) are a bit easier to store than potatoes but aren't terribly space efficient with regards to calories and protein.
All this said, grains and tubers have sustained mankind for eons, so any gardener interested in meeting their caloric needs might want to explore growing all of them. Your own dietary preferences should be considered...grow what you like to eat!!!
Enjoy!
Mike