Stubble height affects the grain yield of ratoon rice under rainfed conditions

Rice ratooning system is becoming an important rice planting system to ensure food security in China, and improvement of grain yield and yield stability has always been the primary goal in the development of ratoon rice. Here, field experiments were conducted in central China from 2020 to 2021 to explore the effects of water management (flooded vs rainfed) and stubble height (45, 20 and 0 cm; abbreviated as SH₄₅, SH₂₀ and SH₀, respectively) on the yield performance of ratoon rice. The results demonstrated that water management during the main season had no effect on the grain yield of either main crop (MC) and ratoon crop (RC). However, rainfed treatment during the ratoon season significantly decreased the RC yield by 14.4% and 9.2% in 2020 and 2021, respectively. The reduction of stubble height prolonged the growth duration, decreased the panicle number, and increased the spikelets panicle⁻¹, total spikelets and leaf area index. Compared with SH₄₅, SH₂₀ and SH₀ increased the RC yield by 20.7% and 6.8% in 2020, respectively, whereas no significant difference in RC yield was observed among different stubble heights in 2021. Moreover, the grain yield of RC at low stubble heights was more susceptible to rainfed treatment. Specifically, rainfed treatment averagely decreased the RC yield by 4.9%, 12.7% and 17.2% at SH₄₅, SH₂₀ and SH₀, respectively. The grain yield of RC was positively correlated with the panicle number, total spikelets and biomass accumulation, while low stubble heights, particularly SH₂₀, had a greater magnitude of slope. Furthermore, panicle number exhibited stronger correlations with spikelets panicle⁻¹ and biomass accumulation at low stubble heights. Overall, our results suggest that more attention should be paid to water management in the ratoon season, and increasing the panicle number is crucial to the improvement of yield and yield stability of RC at low stubble heights.