Crop yield response to water - Cra

and 6-8 tonne/ha in the wet season. Good yields of long duration (120-150 days) cultivarsin subtropical and temperate climates are around 12 tonne/ha, while maximum yields of upto 17 tonne/ha have been reported (Yunnan province in China, and in Australia), althoughsuch reported record yields are often open to question. Significant yield improvement hasrecently come only from the development of hybrid rice, which has increased yield potentialby 5-15 percent over inbred cultivars in the same environment (Peng et al., 1999). Lowland ricewith uncontrolled flooding has average yields of around 1.5 tonne/ha, most likely the resultof occasional water deficit, as well as deprivation of oxygen supply when flooded excessively.For good conditions yields of rainfed lowland rice average 4-5 tonne/ha. With frequent abioticstresses (mainly drought), however, yields are considerably lower, only around 2 tonne/ha.Average upland rice yields are around 1 tonne/ha, while aerobic rice with application ofaround 90 kg N/ha can reach 4-6 tonne/ha.HI varies with cultivar, location, season, and growth conditions. HI of modern, short-durationtropical cultivars is about 0.45 to 0.5 (45 to 50 percent) in the dry season and 0.35 to 0.4 inthe wet season. The HI of many long-duration cultivars used in rainfed lowlands is about 0.35.HI of modern hybrid rice in China range from 0.4 to 0.5. With drought, HI decreases and canreach close to zero in extreme situations.110crop yield response to water