Abstract: Rubber plantations have increased significantly under unprecedented economic growth in tropical areas, which leads to soil degradation and thereby alters soil hydrological processes. However, our understanding of how forest conversion affects soil hydrological processes remains unclear. Here, we collected soil samples from secondary forests (SF) and rubber plantations (RP) to determine the soil hydrological characteristics. We found the topsoil (0-20 cm) water retention in SF was higher than that of RP but displayed the contrast pattern in a deeper soil layer (20-60 cm). Meanwhile, the soil infiltration rates among two vegetation types decreased significantly with infiltration time, with higher stable soil infiltration rates in SF than those in RP. Moreover, soil properties were also impacted by the forest conversion, such as the topsoil capillary porosity and total porosity in SF were higher than those of RP but contrasted in a deep soil layer. In comparison, the topsoil bulk density in SF was lower than that of RP, but contrasted in the deep soil layer and reached a significant level in the 0-10 cm and 40-50 cm (P<0.05). Overall, the soil water retention was mainly determined by the capillary porosity, which could explain 31.56% of total variance in soil water retention, followed by total porosity (26.57%) and soil bulk density (26.47%), whereas soil texture exerts a week effect on soil water retention. Therefore, we can conclude that the conversion of tropical rainforest into rubber plantations may accelerate soil erosion owing to its lower soil water retention and soil infiltration rates.

Key words: soil water retention, soil infiltration, soil physicochemical properties, rubber plantations, secondary forest