Breaking rice yield barrier with the ratooning method under changing climatic conditions: A paradigm shift in rice-cropping systems in southwestern Japan

Rice (Oryza sativa L.) ratooning has recently attracted attention since it possesses higher yield potential compared to conventional rice-growing methods; however, it requires a longer growing season. Field experiments were conducted in southwestern Japan in 2017 and 2018 to determine the effect of harvest time (early and normal) and cutting height (high and low) of the first crop on grain yield of the first and second crops using a high-yielding line under high N application and high air temperature conditions in rice ratooning. The highest total yield of the first and second crops was produced when the first crop was harvested at the normal time with the high cutting height in 2018. This yield reached 14.4 t ha(-1), which is equivalent to threefold the average yield achieved by Japanese farmers. Plants harvested at the high cutting height produced higher grain yield of the second crop because of the larger spikelet number m(-2) and better grain filling using abundant leaf area index (LAI) and nonstructural carbohydrate (NSC) in the stubble. In southwestern Japan, the daily mean air temperatures during the early growth stage of the first crop and the late ripening stage of the second crop have been increasing over time. Our results suggest that increasing LAI and NSC in the stubble by harvesting at the normal time harvest with the high cutting height under high level N application conditions may provide an adaptive strategy to increase yield with a rice-ratooning system as growing seasons extend due to global climate change.