A hybrid variable flux irrigation model for mitigating agroecological impacts of straw incorporation and furrow ridge system in rice-wheat rotations

Shifting from traditional puddled transplanted rice to mechanized drilled-seeding, combined with rotary straw mixing and furrow irrigation, has proven to be a crucial strategy for reducing methane emissions while optimizing resource utilization and productivity. However, this technique introduces other challenges, such as furrow runoff and soil erosion, which contribute to the degradation of ridge/bed soil quality, fertilizer loss, and transport of agroecological pollutants. Therefore, this study explores a hybrid variable flux irrigation (VFI) model as a decision support tool to mitigate these limitations by controlling soil anoxia and runoff in furrow-irrigated rice after straw incorporation. The approach integrates the Hydrus 2D/3D with optimal loop controllers to adjust pump operations based on specific soil moisture levels, variable flux, and furrow water flow depths. Experimental validation and a field case study were conducted in Babaiqiao, Nanjing City, China, where rotary straw mixing and furrow-ridge layouts were applied alongside dry rice seeding and soil hydraulic experiments. The performance indicators of the Hydrus 2D/3D variable flux demonstrated reliable simulation of lateral wetting rates and soil moisture content with R² of 0.79 and 0.89, corresponding RMSE values of 7.90 % and 7.60 %, and MRE values of 1.85 m/day and 0.07 cm³/cm³, respectively. The VFI model proved effective, indicating that the optimal irrigation schedule consisted of three distinct supply regimes. During each cycle, the pump operated intermittently, running for approximately 2.66 hours. VFI led to a 33 % reduction in pumping energy costs while simultaneously mitigating soil anoxia and furrow runoff, thus a potential to reduce the environmental footprint of rice-wheat rotations. Although rice yields under drilled seeding were reduced by 9.56 % compared to flood irrigation due to heavy weed infestation, the VFI model provides valuable insights for promoting straw incorporation and implementing practical solutions that support optimal water utilization and sustainable productivity.