Comprehensive illustration of the improvement of soil conditions and rice production through paddy-upland rotations for sustainable agricultural development

Paddy-upland rotations are promising methods to improve land utilization and grain production and play crucial roles in sustainable agricultural development. However, their effects on soil conditions, rice development, and economic benefits have not yet been systematically investigated. In this study, we investigated the effects of 7 years (2016–2022) of continuous rotation of rice fallow (R-F), rice-rapeseed transplanting (R-tRS), rice-wheat (R-W), and rice-rapeseed direct seeding (R-dRS) on: 1) rice production; 2) key enzymes and genes related to grain starch biosynthesis during the filling stages; 3) paddy soil physiochemical properties, soil enzyme activities, and microbes; and 4) annual economic benefits. Our results showed that 7 years of continuous rotations, especially rice-rapeseed rotations, helped improve soil quality by increasing the organic matter, total nitrogen content, soil sucrase, phosphatase, urease, dehydrogenase, and cellulase, and inhibiting the decrease in pH, available nitrogen, and phosphorous contents. Benefitted by the improved soil conditions, R-dRS showed the highest rice yield of 7800.3 kg·ha⁻¹, revealing increases of 14.3, 4.8, and 6.3 % compared with R-F, R-tRS, and R-W, respectively, mainly owing to the increase of effective panicle numbers. Moreover, the grain starch contents also increased owing to the increase of starch-biosynthesis-related enzymes activities and gene expression in the filling stages; consequently, R-dRS resulted in the most gross margins of 1676.5 dollars·ha⁻¹, with increases of 74.9 %, 14.9 %, and 19.7 % compared with R-F, R-tRS, and R-W. Furthermore, key microbes closely related to soil properties and traits of rice yield were identified using the liner discriminant analysis (LDA) effect size (LEfSe) and Mantel methods after bacterial 16S and fungal ITS sequencing. In conclusion, we validated the advantages of paddy-upland rotation, especially R-dRS, in terms of soil improvement, plant growth, and economic benefits. The longitudinal variation trends of annual soil physiochemical properties, key microbes, and the influence of improved soil conditions on rice grain filling were identified, providing a theoretical basis for food security and sustainability.