Root-soil-water interaction process and its mechanism in saline agriculture in the Yellow River Delta

Coastal saline agriculture in the Yellow River Delta (YRD, China) is constrained by salt accumulation driven by shallow groundwater–evaporation coupling and by mechanical limitations imposed by soil compaction. Because soil strength and pore connectivity control root penetration, aeration and preferential flow, root–soil–water interactions in the YRD are inherently hydro-mechanical. We ask how depth-dependent compaction reorganizes water–salt dynamics and root system architecture.

We integrate multi-season field experiments, controlled “transparent-soil” microcosms, and coupled modelling. In the field, three compaction levels (non-, light- and heavy-compacted) are crossed with contrasting tillage (mouldboard ploughing, rotary tillage and no-till) and crop types (soybean/maize rotation and winter wheat). Soil water content, electrical conductivity, temperature and matric potential are monitored at multiple depths. Soil mechanical state (penetration resistance and bulk density) and key hydraulic functions (water retention) are measured on undisturbed samples, while root traits are quantified by excavation and image analysis. Microcosms tune substrate stiffness via hydrogel crosslink density to isolate mechanical impedance effects; the datasets are interpreted using flow–transport simulations linking root uptake, water flow and salt movement.

Preliminary results show that heavy compaction can increase short-term near-surface water storage after rainfall but restricts rooting to the upper 0–10 cm, decreases aeration and intensifies salinity stress, causing marked biomass and yield losses. In contrast, moderate compaction combined with conservation practices reshapes preferential flow and capillary return, moderating salt accumulation while maintaining root penetration. Microcosms reveal a mechanical “optimal window” where roots maximize elongation and branching; both insufficient strength (unstable pore network, hypoxia) and excessive strength (high impedance) suppress root exploration.

Overall, we identify a feedback loop in which soil strength controls rooting depth and biopore formation, which in turn reorganizes pore connectivity and preferential flow, ultimately governing salt leaching and capillary re-salinization. The framework supports targeted mechanical management (hardpan alleviation, controlled traffic and structured surface–subsurface layering) for resilient saline agriculture in the YRD.