Worldwide 79 million hectares of irrigated lowlands provide 75 percent of the world’s rice production.  At the turn of the Millennium, the country’s average irrigated rice yields in Asia ranges from three to nine tons per hectare, with an overall average of about five tons per hectare

Irrigated rice is mostly grown with supplementary irrigation in the wet season, and is entirely reliant on irrigation in the dry season. Significant areas of rice are grown in rotation with other crops.

Irrigation systems vary widely, and include:

Click each text to view a sample picture. 

Individual pump irrigation from shallow tubewells (down to about 15 m depth)

Small to medium scale community-based pump irrigation from deep wells (down to 200-300 m depth)

Small to medium scale commmunity-based surface irrigation where water is derived from pond or reservoirs

Small to medium scale community-based surface irrigation where water is directly diverted from a river (run-of-the-river irrigation)

Large-scale surface irrigation where water is diverted from reservoirs or lakes

After knowing the common types of irrigation systems, you can now proceed in understanding the water balance in the rice field.