Secondary Forest Conversion Into Betel Nut Plantations Reduces Soil Water Retention by Altering Soil Properties.

Betel nut plantations have rapidly expanded in recent decades owing to their considerable economic benefits, resulting in a significant reduction of tropical secondary rainforests, which has had substantial impacts on soil hydrological properties. However, few studies have investigated the effects of forest conversion on these properties. In this study, soil samples from secondary forests (SF) and betel nut plantations (BP) were collected to assess soil physicochemical and hydrological properties. The results showed significantly higher topsoil (0-10 cm) water content and saturated water-holding capacity in SF than in BP. However, the opposite pattern was observed in the subsurface soil layer (20-60 cm). Similarly, the 0-10 cm soil layer showed higher capillary water capacity and field capacity in SF than in BP, but this trend was reversed in the 10-60 cm soil layer. Additionally, the conversion of forests into betel nut plantations led to a reduction in saturated hydraulic conductivity. The soil hydrological properties were significantly affected by land-use change through alterations in soil properties. We found that the soil nutrient content in BP was much lower than that in SF. Besides, soil capillary porosity played a role in influencing soil water retention, accounting for 32.03% of the variation, followed by total porosity (27.04%) and soil bulk density (26.5%), whereas the soil particle composition also had a resistance to soil degradation effect on soil water retention. Together, the conversion of secondary forest into betel nut plantations not only led to soil degradation, but also has negative effects on soil water retention capacity by reducing soil porosity and increasing soil bulk density. These findings provide important insights for the management of agroecological systems in tropical regions.