[awesome_dude]

It's my understanding that corn produces the most (edible) calories per square metre of any of our farmed plants

edit: Looked it up - Rice has the highest number of calories per square metre of farmland, just that it requires marshy/swamp land to grow.

[lovemenot]

There are many varietals of rice. Most do not grow in marsh land. Farmers often do flood the fields at the beginning of a rice growing season in order to drown out any competing plants. Flooding is not necessary though. Rice will grow with normal irrigation.

[phanimahesh]

Yes. Rice tolerated flooding better than weeds so it is used as a cheap and easy weed control. Also some places grow fish alongside rice in the same land, getting some extra pest control and fertilizer for free.