Optimizing the C/N ratio of straw increases rice yield and stability by the enhanced soil-root interaction

Soil degradation poses a significant threat to agricultural sustainability and food security, with straw incorporation emerging as an effective measure for sustainable agricultural development. However, the synergistic effects of adjusting straw carbon-to-nitrogen (C/N) ratios on soil quality and rice root systems remain unclear. To address this knowledge gap, we conducted a four-year field experiment employing a single-factor randomized block design. Conventional cultivation (CK) was used as the control, and five treatments were established under straw incorporation conditions: no nitrogen application (SN0) and four C/N ratios of 35:1 (SN1), 31:1 (SN2), 27:1 (SN3), and 23:1 (SN4). The study aimed to investigate the impact of regulating straw C/N ratios on soil quality, root growth, and yield, while elucidating their interrelationships. Results demonstrate that straw incorporation significantly enhances the soil quality index, with improvements ranging from 58.51 % to 173.79 %. Low C/N treatments mitigate the inhibitory effects of straw incorporation on root growth during the tillering stage and promote mid-to-late stage root development through soil quality optimization, leading to a significant 10.74 % yield increase in SN3. Linear regression analysis reveals a significant positive correlation between the soil quality index and the sustainability yield index. Partial least squares path modeling indicates that soil biological properties are the primary drivers, directly influencing the soil quality index and indirectly affecting rice yield. Various indicators exhibit unimodal responses with decreasing C/N ratios, reaching a threshold at SN3. In conclusion, SN3 achieves a synergistic enhancement of the soil quality index and root growth, consequently improving rice yield and stability. These findings provide valuable guidance for enhancing soil quality and developing sustainable agriculture.