Rice Adaptation to Aerobic Soils: Physiological Considerations and Implications for Agronomy

Abstract

Aerobic culture is a water-saving technique for direct-seeded rice cultivation. Growing rice under continuously unsaturated soil conditions can maximize water-use efficiency and minimize both labor requirements and greenhouse-gas emissions. Under a temperate climate, aerobic culture can produce a rice yield greater than 9 t ha^-1 especially in central Japan (11.4 t ha^-1). Aerobic culture using large-scale center-pivot sprinklers is being established in the central United States, where yields can surpass 10 t ha^-1. However, yields remain at less than 8 t ha^-1 in the tropics. The high yield of Japanese aerobic culture is mainly attributed to vigorous nitrogen uptake during the reproductive stage, which allows rice plants to produce more spikelets and biomass. Fertilizer management for aerobic culture must satisfy both the nitrogen demand and control spikelet density to achieve an appropriate sink-source balance. Unfortunately, the poor development of the root system in rice limits its water uptake from unsaturated soil. Adaptive responses such as adventitious root emergence, lateral root branching, and deep root penetration would protect the plants against dehydration stress in aerobic culture. Intermediate plant height with a few large tillers rather than semi-dwarf stature with profuse tillering should be a suitable plant type for aerobic culture, and plants should show leaf expansion despite fluctuations of soil moisture. The development and identification of suitable genotypes and crop management options are underway worldwide for more resource-use efficient and productive aerobic rice culture.