How sustainable is aerobic rice?
Given assured water supply, lowland rice fields are extremely sustainable and able to produce continuously high yields, even under continuous double or triple-cropping a year. Flooding of rice fields has beneficial effects on soil acidity (pH), soil organic matter buildup, phosphorus, iron, and zinc availability, and biological N fixation that supplies the crop with additional N. When fields are not continuously flooded, such as in aerobic rice, these beneficial effects gradually disappear. A change from flooded to aerobic soil conditions may decrease the soil organic matter content, decrease the soil pH, and decrease the availability of phosphorus, iron, and – on calcareous soils - zinc. Also, problems with micro-nutrient deficiencies have been reported. If field were cropped to rainfed rice with alternate periods of flooding and dry soil, or if fields were previously cropped to upland crops, then the introduction of aerobic will have fewer consequences for these sustainability parameters.
There are indications that soil-borne pests and diseases such as nematodes, root aphids, and fungi occur more in aerobic rice than in flooded rice, especially in the tropics. The current experience is that aerobic rice should not be grown continuously on the same piece of land each year (as can be successfully done with flooded rice) without yield decline. Suitable crop rotations need to be identified, but will be site-specific and responsive to markets.
Current research focuses on determining the causes of yield decline under continuous cropping (biotic, abiotic), on developing “resistant” varieties, on developing suitable management options such as crop rotation, and on developing integrated weed management practices.