Evaluation of tradeoffs in land and water productivity of dry seeded rice as affected by irrigation schedule

Management strategies that increase water productivity and reduce labour requirement while maintaining or increasing land productivity are urgently needed. Dry seeded rice (DSR) has been proposed as one of the technologies to achieve these objectives, but little is known about tradeoffs between land and water productivity of rice as affected by irrigation schedule. This study tested the ability of the ORYZA2000 model to simulate the effects of irrigation schedule of DSR on yield, various measures of water productivity, and soil water dynamics. The study showed that under conditions of no or mild water stress (up to 20 kPa SWT) ORYZA2000 performs well in simulating the effects of irrigation schedule on crop growth, yield, soil water dynamics, water balance components and water productivity of DSR in north-west India. However, the model overpredicted crop growth and yield at higher irrigation thresholds (40 and 70 kPa) which was atleast partially due to the fact that the DSR suffered from iron deficiency at higher irrigation thresholds.Using weather data for 40 rice seasons, the model predicted that there is always some yield penalty when switching from continuous flooding (CF) to alternate wetting and drying (AWD) of DSR. The yield decline varied from 6% with an irrigation threshold of 10 kPa to 26% at 70 kPa. However, there was large irrigation water saving when changing from CF to alternate wetting and drying (AWD) at only 10 kPa, and only a small rate of decline in irrigation input as the threshold increased from 10 to 70 kPa. The water saving with AWD was primarily because of less drainage. There were tradeoffs between yield, water productivity and water depletion in relation to irrigation schedule. Maximum yield occurred with CF, maximum WPI and WPI+R with an irrigation threshold of 30 kPa and maximum WPET with a threshold of 20 kPa.

► ORYZA2000 performed well for dry seeded rice generally up to 20 kPa.
► Yield declined steadily as soil dried from saturation to 70 kPa irrigation threshold.
► There were tradeoffs between yield, WPI and WPET.
► The irrigation water saving in AWD was primarily due to less drainage.
► Maximum WPI achieved with DSR-30 kPa while maximum WPET achieved with 20 kPa.