Regulatory effects of terracing and intercropping on soil moisture infiltration characteristics in rubber plantations

Objective This study aims to investigate the effects of terracing and tea intercropping on soil water infiltration processes and the development of preferential flow in rubber plantations. The objective is to provide empirical data and scientific evidence to support water management and sustainable land use in tropical rubber-growing regions.

Method A brilliant blue FCF dye tracer technique was used to conduct a comparative analysis of four typical rubber planting patterns: rubber-tea agroforestry on terraces, rubber monoculture on terraces, rubber-tea agroforestry on flatland, and rubber monoculture on flatland. By comparing combinations of different topographies (terrace vs. flatland) and stand types (agroforestry vs. monoculture), key parameters were quantified, including maximum dye penetration depth (M_DD), total dyed area (A_TD), uniform infiltration depth (U_ID), length index (I_L), and dye coverage (D_C), to assess infiltration patterns and preferential flow characteristics. The regulatory effects were comprehensively analyzed using permutation tests (α = 0.1), Bootstrap 95% confidence intervals (95% CI), and Cohen’s d effect sizes.

Result (1) Topography significantly influenced M_DD, A_TD, and I_L (p < 0.1, 95% CI excluding zero, |d| > 0.8). Under the same stand type, terraced rubber plantations exhibited 11.3%–69.6% higher M_DD, 5.0%–70.7% higher U_ID, 39.0%–63.2% higher A_TD, and 12.6%–19.3% lower I_L than flatland plantations. These findings indicate that terracing promotes deeper infiltration dominated by matrix flow. (2) Stand type significantly affected M_DD and A_TD (p < 0.1, 95% CI excluding zero, |d| > 0.8). Under the same topography, rubber-tea agroforestry demonstrated 3.6%–36.8% lower M_DD, 3.4%–40.6% lower U_ID, 30.1%–40.5% lower A_TD, and 7.7%–16.6% higher I_L relative to rubber monoculture. These results suggest that tea intercropping facilitates localized infiltration through more developed preferential flow paths, while the shallow root system of tea intercepts water in the upper soil layers, thereby limiting overall infiltration depth.

Conclusion Topographic modification alters slope morphology, providing physical pathways that enhance deeper soil water movement and significantly improve matrix flow processes and vertical infiltration capacity. Stand type influences root distribution, soil pore structure, and biological processes, thereby regulating the formation of preferential flow paths and the retention and redistribution of shallow soil moisture. These factors interact structurally and functionally, jointly influencing soil water infiltration routes and transport dynamics in rubber plantations. Overall, topography, as a large-scale physical factor, predominantly governs water flow paths and moisture redistribution, demonstrating a significant and robust regulatory effect. This study reveals a regulatory framework for soil water infiltration in rubber plantations that is primarily driven by topography and modulated by stand type.