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Because of increasing competition for water, water-saving technologies such as alternate wetting and drying and aerobic rice are being developed to reduce water use while maintaining a high yield of rice. The components of the water balance of these systems need to be disentangled to extrapolate water savings at the field scale to the irrigation system scale. In this study, simulation modelling was used to quantify yield, water productivity, and water balance components of alternate wetting and drying and aerobic rice in the conjunctive surface-groundwater Liuyuankou Irrigation System, Henan, China. The study on aerobic rice was supported by on-farm testing.
In the lowland rice area, where groundwater tables are within the root zone of the crop, irrigation water savings of 200�900 mm can be realized by adopting alternate wetting and drying or rainfed cultivation, while maintaining yields at 6400�9200 kg ha-1. Most of the water savings are caused by reduced percolation rates, which will reduce groundwater recharge and may lead to decreased opportunities for groundwater irrigation. Evaporation losses can be reduced by a maximum of 60�100 mm by adopting rainfed cultivation. In the transition zone between lowland rice and upland crops, groundwater tables vary from 10 cm to more than 200 cm depth, and aerobic rice yields of 3800�5600 kg ha-1 are feasible with as little as two to three supplementary irrigations (totaling 150�225 mm of water). Depending on groundwater depth and amount of rainfall, either groundwater recharge or net extraction of water from the soil or the groundwater takes place
