Low light stress increases the chalkiness of rice; however, this effect has not been fully characterized. In this study, we demonstrated that low light resulted in markedly decreased activity of ADP-glucose pyrophosphorylase in the grains and those of sucrose synthase and soluble starch synthase in the early period of grain filling. Furthermore, low light also resulted in decreased activities of granule-bound starch synthase and starch branching enzyme in the late period of grain filling. Therefore, the maximum and mean grain filling rates were reduced but the time to reach the maximum grain filling rates and effective grain filling period were increased by low light. Thus, it significantly decreased the grain weight at the maximum grain filling rate and grain weight and retarded the endosperm growth and development, leading to a loose arrangement of the amyloplasts and an increase in the chalkiness of the rice grains. Compared to the grains at the top panicle part, low light led to a greater decrease in the grain weight at the maximum grain filling rate and time to reach the grain weight at the maximum grain filling rate at the bottom panicle part, which contributed to an increase in chalkiness by increasing the rates of different chalky types at the bottom panicle part. In conclusion, low light disturbed starch synthesis in grains, thereby impeding the grain filling progress and increasing chalkiness, particularly for grains at the bottom panicle part.

Few studies have tested the influence of climatic factors on yields by adjusting sowing dates at both low and high altitudes. We investigated the influence of the synergistic effects of temperature and solar radiation by conducting field experiments using different rice varieties and sowing dates in the low-altitude plains of Chongzhou and the high-altitude mountainous region of Hanyuan, Sichuan Province, China, in 2017 and 2018. The results showed that from transplanting to maturity, biomass yield and grain yield were significantly (p < 0.01) correlated with the average daily temperature and solar radiation. The Hanyuan site experienced higher solar radiation and lower temperature than those of Chongzhou, which contributed to higher dry matter accumulation (DMA) and crop growth rate values pre- and post-anthesis and more panicles per m², leading to higher biomass yields and grain yields at Hanyuan. The rice sowed earlier was subjected to higher solar radiation and lower temperature at Chongzhou and Hanyuan, resulting in increased DMA post-anthesis, panicles per m², and spikelet filling, improving biomass yield and grain yield. These results indicate that the high potential yield from the early sowing date in the high-altitude region was primarily due to increased solar radiation and decreased temperatures.

Sowing quality is directly influenced by the seed-filling characteristics of a centralized seed-metering device, and vigorous seed-motion status deteriorates seeding performance resulting from field surface roughness, seeder vibration, etc. However, the relationship between vibration and seed-filling properties remains unclear. This study measured the vibration characteristics of a seed-metering device, examined unmeasurable seed-motion characteristics based on DEM simulation, and used bench tests to determine the seed-filling characteristics under vibration conditions. The frequency distribution of the rapeseed seeder was 0–180 Hz. The simulation results revealed that the vibration mainly changed the level of seed in the seed-filling area; moreover, it significantly increased the seed-filling angle, ranging from 56.00°–59.00° to 69.78°–91.40°, which affected the seed-filling performance. A vibration frequency of 10–40 Hz resulted in a target seed rate within 88.67–99.44%, but when there is no vibration, the target seed rate reached 100%. The bench test results demonstrated that the seed-filling angle under vibration will increase with an increase in longitudinal distance, and will change between 15.49°–102°. The seed-filling performance affected by longitudinal distance was larger than that affected by lateral distance. By adjusting the longitudinal distance to range from 0–20 mm, the target seed rate could be maintained above 91%. The findings help to improve our knowledge of seed-filling characteristics under vibration conditions, and should be conducive to improving seeding performance by adjusting the seed layer height to reduce the impact of vibration on field operations.