Dynamic interplay between preferential and matrix flows enhances water circulation in rubber agroforestry soil profiles

Jiang, Xiao-Jin

SOIL & TILLAGE RESEARCH

2026

257

Jiang, XJ;Lin, YX

Spatial variations in preferential and matrix flow play a critical role in the key processes related to ecohydrology, soil and water conservation, and groundwater pollution. However, the interactions between preferential and matrix flow in regulating water and solute transport through soil profiles remain inadequately understood, especially under the alternating rainy and dry seasons of tropical regions. In this study, we investigated how alternating mechanisms of preferential and matrix flow influence soil water storage in southwestern China. We used ecological bistable theory and in-situ field measurements across rubber-related forest systems with different root biomass (increasing in the following order: rubber monoculture (RM) < rubber-Alpinia oxyphylla (RAO) < rubber-orange-tea (ROT) < artificial rubber rainforest (ARR)). The results show that the soil water storage in RM to RAO, ROT, and ARR increased by 18 %, 23 %, and 31 %, respectively. These increases were strongly associated with soil total porosity (R-2 = 0.933), saturated hydraulic conductivity (K-s) (R-2 = 0.879), and water flow behavior (R-2 = 0.968). The dominant water flow behaviors during the alternating rainy and dry seasons were high-low levels of matrix flow and low level of preferential flow in RM, and high-low levels of preferential flow and high level of matrix flow in ROT and in ARR. An opposite relationship occurred between preferential and matrix flows, with matrix flow exhibiting a sinusoidal pattern at the annual scale. Preferential flow dominated downward water flow in the rainy season (contributing similar to 13 %, 58 %, 61 %, and 72 % in RA, RAO, ROT, and ARR), whereas matrix flow dominated upward water flow in the dry season (accounting for 33 %, 62 %, 73 %, and 76 %, respectively). The interaction between preferential and matrix flows formed a bidirectional water movement throughout the soil profiles, enhancing water transport and storage across the forest systems, which increased in the order of RM < RAO < ROT < ARR. This study elucidates the bistable dynamics between preferential and matrix flows in rubber-related forests, offering insights for balancing rainwater utilization and intercropping design in rubber-based agroforestry management.