Synergistic effects of magnesium fertilisation and machine-transplanting density improve rice yield and grain quality

To clarify the regulatory mechanisms and optimal combinations of magnesium fertiliser application rates and machine-transplanting density on rice yield, quality, and magnesium uptake and utilisation in the hilly regions of Sichuan. This study utilised a two-factor split-plot design in field trials conducted from 2024 to 2025. The main plot was magnesium application rate, with four treatments: 0 kg/ha (Mg0), 30 kg/ha (Mg1), 45 kg/ha (Mg2), and 60 kg/ha (Mg3). With the secondary factor being machine-transplanting density, comprising three treatments: 14 cm × 30 cm (D1), 18 cm × 30 cm (D2), and 22 cm × 30 cm (D3). The study investigated the effects of interactions between magnesium fertiliser application rates and planting density on rice yield components, leaf physiological characteristics, dry matter transport, and magnesium fertiliser use efficiency. The results showed that, compared with the Mg0 treatment, the Mg3 treatment significantly increased rice yield, with the best results observed in combination with the D1 treatment, yielding a 14.52% increase over the Mg0 treatment. Dry matter transport in rice increased significantly with the application of magnesium fertiliser. Compared to the Mg0 treatment, the Mg3 treatment increased stem and leaf dry matter transport by 19.64%, and post-heading dry matter transport by 30.76%; the D1 treatment further optimised dry matter transport. Compared to the D3 treatment, the amount of stem and leaf dry matter transport, the transport rate, and the contribution rate to grain increased by 26.44, 34.28, and 40.32%, respectively. Magnesium uptake and utilisation efficiency were highest under the Mg3 treatment. Compared to the Mg0 treatment, magnesium uptake and utilisation efficiency increased by 31.25%, and the physiological utilisation rate of magnesium fertiliser increased by 24.71%; under the D1 treatment, the agronomic utilisation rate and uptake and utilisation efficiency of magnesium fertiliser increased by 38.22% and 20.20%, respectively, compared to the D3 treatment. Furthermore, the Mg3D1 treatment significantly increased the rice leaf area index and chlorophyll content, while simultaneously improving rice processing and appearance quality and reducing chalkiness and amylose content. This series of measures achieved synergistic optimisation of magnesium fertiliser application rates and machine-transplanting density.