How many pounds of rice does it take to feed a person for a year?

If we're talking about grain in terms of rice (grains would include rice, corn, wheat, barley, rye, oats, and rice) one cup of cooked, white rice provides about 205 calories. A subsistence diet of 1,200 calories a day would mean you would need to eat six cups of cooked rice a day to survive, barely. 1-1/2 cups of dried rice would equal about six cups of cooked rice.

If we look at wheat flour, one cup of wheat flour has about 400 calories, so again, a subsistence diet of 1,200 calories a day would require three cups of flour. However unlike rice, flour is usually prepared with oil to make it more edible, as flour and water is basically like eating wallpaper paste.

If we look at oats, and use whole grain oats that are not processed for fast cooking, one dry cup has 600 calories, so you would need two cups a day on a 1,200 calorie subsistence diet.

One small ear of corn has just 63 calories (with no butter or anything else added). You'd have to eat about 20 ears of corn a day to survive. If it was processed as cornmeal, you would need about three cups a day. Even more so than flour, cornmeal would be very hard to eat without adding other calories to it like oil or other fats.

None of these alone will provide a balanced diet and basic nutrition. Someone doing physical work or hard labor would not be able to survive on 1,200 calories a day.