[nbernard]

According to Braudel (in Civilization and Capitalism, 15th-18th Century, vol. 1), without irrigation rice farming depletes the soil much, much more than wheat. If I remember correctly, he states that if one waits for natural soil regeneration (fallowing and/or crop rotation) wheat can be grown at the same place every 2 to 3 years, whereas for rice it is only every 10 to 30 years.

[kelipso]

Comparatively, with irrigation and good weather you could harvest rice usually 3 and up to 4 times a year in south of India.