You need to eat. No matter the situation, you need to eat, and in some cases it’s imperative that you do to keep your strength up. A large portion of our diet is (generally) made up of carbohydrates, so it’s obviously important to find a source of carbohydrates. If you’ll be doing a lot of manual labour, carbs are especially important to keep your energy up.
Let’s assume you have some land and some equipment. You even have some seeds to plant. How much do you plant to sustain yourself?
Going back to daily caloric requirements, you’ll see that one person will need about 370g of carbohydrates a day. If you’re in dire straights, you could eat nothing but grains, but that wouldn’t be good for you in the long run. Nevertheless, let’s assume you really like fresh bread, and round that 370g/day up to 400g, which translates into 1000g of actual grain products you need to eat.
So, 1kg/day. As you’ll likely only get one growing season, you’ll need to harvest your annual carb intake all in one season. That means 365kg per person per harvest. So, how much do you plant to get that kind of a harvest?
[What’s with all the circles? A circle is the way to enclose the most area with the least perimeter. If you’re going to fence your crop, a circle will use the least amount of fence per area enclosed.]
Please note that despite my research, this may not be a good representation of what your yields will be. This data is from commercial farming, using big equipment, fertilizers, chemicals, the whole nine yards. You’ll likely be simply using yourself. Expect lower yields typically, although who knows what good effects the use of chicken manure will have on your crop, or the use of heartier natural grain varieties.
For a much more authoritative article on grains, look at Mother Earth News’ archives.