Is aerobic rice rainfed or irrigated?
Like wheat or maize, aerobic rice can be rainfed, supplementary irrigated, or fully irrigated. With groundwater tables below the rootzone, a suitable total amount of water supply by rainfall and/or irrigation is probably 600-800 mm over the growing season. With deep groundwater tables and less than 400 mm, the typical traditional upland rice system with sturdy and drought-resistant upland varieties is more suitable. When subsurface hydrology, soil type, and rainfall (and/or irrigation) combine to create predominantly flooded or saturated soil conditions throughout the growing season, the typical lowland rice production system is more suitable. With clayey soils and groundwater tables below the rootzone, one would need typically 1000 mm or more to maintain predominantly saturated soil conditions. However, with groundwater tables within the 20-cm rootzone (as occurs in many typical irrigated lowland rice environments), as little as 400 mm can already maintain predominantly saturated soil conditions or flooding. The exact “transition zones” between upland rice and aerobic rice, and between aerobic rice and lowland rice production systems is therefore quite site-specific.
The optimum soil water condition for aerobic rice is around field capacity. If rainfall is insufficient to frequently restore water contents in the soil to field capacity, irrigation can be applied if water resources are available. Irrigation can be applied through flash-flooding, furrow irrigation (or raised beds), or sprinklers. Unlike flooded rice (lowland rice), irrigation - when applied – is not used to flood the soil but to just bring the soil water content in the root zone up to field capacity. The amount of irrigation water should match evaporation from the soil and transpiration by the crop (plus any application inefficiency losses). In lowland rice, the amount of irrigation water should match the same water flows, plus the losses by seepage and percolation.