Effects of potassium management on potassium accumulation and remobilization characteristics, and utilization efficiency of rice under different light conditions at the grain filling stage

In this study, the effects of potassium (K) management on the accumulation, distribution, and remobilization characteristics of K, and K utilization efficiency of rice under different light conditions were investigated using rice variety ‘F You 498’ as the material. The results showed that the accumulation, distribution, and remobilization characteristics of K in rice were collectively influenced by light conditions and K management. Compared with natural light, low-light stress significantly increased the K content of shoots in 20 days after heading and at maturity, accumulation amount and distribution ratio of K in the top three leaves, and remobilization contribution rate of K in the stem sheath. Low-light stress considerably decreased the amount and rate of remobilization of K, remobilization contribution rate of K in the leaves, and accumulation of K in other stem sheaths and panicles. This resulted in a substantial decrease in the partial factor productivity of K by 18.7%–25.1% in 2021 and 2022. Compared to the no-K treatment, the application of K considerably increased the K content in rice organs. It also boosted the distribution ratio of K in the panicle, and the amount of K remobilization in leaves and stem sheaths. This led to a substantial increase of 42.8%–76.6% in K accumulation in the shoot at maturity. Compared with 90 kg·hm^–2 of K₂O used as basal (K90-0) and panicle (K0-09) fertilizers, 180 kg·hm^–2 of K₂O equally divided into basal and panicle fertilizers (K90-90) increased K accumulation in the top three leaves and shoots by 7.9%–27.4% and 7.7%–24.8%, respectively. Additionally, the K0-90 treatment increased the remobilization amount and rate of K in leaves and stem sheaths, which contributed to increases of 1.1%–2.1%, 18.8%–20.7%, and 9.4%–63.1% in the partial factor productivity, agronomic use efficiency, and physiological use efficiency of K under low-light stress, respectively, compared with the K90-0 treatment. Correlation analysis revealed that the rice yield was significantly and positively related to the K accumulation amount of leaves, K distribution ratio of leaves and panicles at maturity, harvest index of K, remobilization amount and rate of K, and remobilization contribution rate of K in stem sheaths under low-light conditions. The rice yield was significantly and negatively associated with the K distribution ratio in stem sheaths at maturity and recovery efficiency of K under low-light conditions. In conclusion, low-light stress effectively improved the K content of rice organs and inhibited the remobilization of K in leaves, leading to a reduction in the accumulation of K in panicles at maturity and partial factor productivity of K. Meanwhile, the application of K fertilizer, particularly panicle K application, promoted the remobilization of K in the leaves and stem sheaths, thereby enhancing the use efficiency of K under low-light stress.