Jungle rubber facilitates the restoration of degraded soil of an existing rubber plantation

Conversion of forest to rubber plantation is one of the most common land-use change in the humid tropical region. It is one of the fastest expanding farms that lead to various socioenvironmental issues. We investigated the effect of this land-use change on soil physico-chemical properties by surveying different succession stage rubber plantations, including monoculture and a mixture derived by mixing jungle rubber and a reference tropical rainforest. We also assessed the impact on stoichiometric ratios and allocation relationships of soil carbon (C), nitrogen (N), and phosphorus (P). Our results demonstrated that conversion of tropical rainforest to rubber monoculture resulted in serious soil degradation, with a lower level of water content, water holding capacities, total porosity, pH, and soil nutrients, and a higher level of soil bulk density. However, after transforming a rubber monoculture into a jungle rubber, the concentrations of soil total C, N, P, Ca, and Mg significantly increased, by 28%, 24%, 23%, 17%, and 39%, respectively. Meanwhile, soil salinity declined by 15%. Jungle rubber also exerted some desirable effects on soil physical properties, such as decreased soil bulk density, increased field capacity and non-porosity by 6%, 2%, and 33%, respectively. Like other tropical regions, soils in the present study areas are mainly under P limitation, but jungle rubber increased soil P turnover and thereby increases P availability. In conclusion, jungle rubber correcting the soil degradation resulted from rubber plantation on tropical forest soil. Given the improvements in soil quality, constructing multiple-strata and multi-species rubber agroforestry (e.g., jungle rubber) can be a promising approach to facilitate the restoration of the existing monoculture rubber plantations.