Effects of conservation tillage and rainwater harvesting-recharge irrigation on soybean root architecture and yield in cold-region mollisols

Northeast China's agricultural sustainability is currently confronted with dual challenges of progressive soil degradation and uneven precipitation distribution. To address water deficit during critical crop growth stages while maintaining soil conservation, this study implemented a conservation tillage system integrated with Rainwater Harvesting-Recharge Irrigation Gradients (RH-RIG) through field experimentation. A 3 × 4 factorial completely randomized design was adopted, combining three conservation tillage practices (No-till/NT, Reduced tillage/RT, No-till with Mulching/NTM) with four RH-RIG levels (75 %, 125 %, 150 % of natural precipitation, plus rain-fed control/100 %). The experiment investigated the effects of tillage practices and rainwater utilization gradients on soybean root parameters (root length, surface area, volume, mean diameter, root-to-shoot ratio) and yield components. The results showed that: (1) Conservation tillage practices significantly influenced soybean root morphological traits, particularly total root length, root surface area, and root dry matter biomass (p < 0.05), thereby enhancing overall root system development. (2) Root parameters exhibited nonlinear responses to RH-RIG. The 125 % RH-RIG treatment achieved peak root volume and length, while the 150 % treatment reduced traits due to anaerobic stress, suggesting 1 25 % as a more effective water threshold. (3) No interaction was observed between tillage practices and RH-RIG. The combination of NT and 125 % RH-RIG (Treatment A2) independently enhanced root growth through additive physiological effects. (4) Root traits were positively correlated with yield. Treatment A2 produced the highest grain yield (2.97 ± 0.02 t ha⁻¹), representing a 31.6 % increase over the control. This study provides a theoretical foundation for implementing soil conservation-priority strategies and rainwater utilization in agricultural practices within cold-region Mollisol areas, offering critical guidance for enhancing crop productivity. • Conservation tillage and rainwater utilization regulate soybean root architecture and yield. • Rainwater utilization better matches the water needs of crops at critical growth stages with water supply. • Investigated the relationship between root traits of soybeans and yield under the regulation of moisture.