Can intercrops improve soil water infiltrability and preferential flow in rubber-based agroforestry system?

Abstract

Land-use change due to the widespread practice of rubber-based agroforestry influences ecosystem services. However, little is known about their soil hydrological functioning associated with infiltration and water flow behaviour which affects surface runoff, soil erosion, and groundwater recharge. In order to clarify whether the intercrop can promote soil water infiltrability and water movement in rubber-based agroforestry system, 66 field infiltration and 2 dye tracer experiments were performed in this study on undisturbed soil in a rubber-tea agroforestry system in Xishuangbanna, SW China. The results showed that the field saturated soil hydraulic conductivity (Ks) exhibited a high spatial heterogeneity. The Ks, initial infiltration rate (IIR), and actual steady-state infiltration rate (Is) were significantly higher in the tea tree planting zone (TT) than in the rubber tree planting zone (RT). The Ks decreased with distance from the trunks of tea trees, and the Ks between rubber trees in a row was lower than that between rubber rows. Along with improved soil physical properties, increased root and faunal activities, and more inhomogeneous cracks and stones, there was higher soil water infiltrability and more preferential flow in the TT than in the RT. Therefore, tea shrubs in rubber agroforestry systems may function as water harvesters, contributing to deeper drainage and recharge. In contrast, the rubber trees function as water consumers, causing soil desiccation and water scarcity. Differences in the soil hydraulic properties among different zones in a rubber-tea agroforestry system can lead to the spatial redistribution of surface and belowground water, increasing water availability for various plants with different root systems. Better infiltration and increased preferential flow beneath tea trees potentially reduce runoff generation and erosion risk, promote groundwater recharge, and increase water storage that may counteract the interception and transpiration losses from intercrops and rubber trees, thereby contributing to the management of water resources.