Apparently mainly rice growing. I knew paddy fields were bad, but I didn't know they were that bad. Per calorie I am sure it is more like a tenth that of ruminants, perhaps less, but still worth replacing with other carbohydrates.
Complete rice also carry lisine (although less than beans) which is a really hard amino acid to get on a vegetarian diet.
And rice is unusually poor in vitamins and minerals. Even brown rice is nowhere near as good a fiber source as vegetables, fruits, beans, nuts, seeds.
If you want an actually excellent staple crop, buckwheat is about the only truly outstanding one.