Intercropping with cash crops promotes sustainability of rubber agroforestry: Insights from litterfall production and associated carbon and nutrient fluxes

Increasing global demand for natural rubber has resulted in rapid expansion of rubber plantations and subsequent environmental issues in the tropics. Diversified rubber agroforestry (i.e. mixed planting of rubber with various crops) are proposed to counteract negative effects induced by rubber monoculture (RM). However, little is known about the changes in ecosystem function and services associated with biogeochemical cycles following RM conversion to rubber agroforestry. A three-year study was conducted to investigate litterfall biomass, stand litter and nutrient return in RM and three rubber agroforestry systems, i.e., rubber-tea (RTAs), rubber-Flemingia macrophylla (RFAs), and rubber-cacao (RCAs). Annual litterfall production was the highest in RCAs (8.92 Mg ha–1 yr–1), followed by RTAs (8.25 Mg ha–1 yr–1), RFAs (7.30 Mg ha–1 yr–1), and the lowest in RM (5.42 Mg ha–1 yr–1). Temperature, relative humidity, and solar radiation were dominant drivers of the distinct seasonality of litterfall production, with most of production (64–71%) occurring in the dry and cold season. Average stand litter showed the decreasing order of RTAs > RCAs > RFAs > RM. Litter turnover rate was generally lower in RM than in rubber agroforestry systems. Carbon and nutrient returns via litterfall exhibited 1.3–1.6 times higher in rubber agroforestry than in RM. RM had the greatest P use efficiency due to low P availability in the soil. Such strong P limitation was mitigated by introducing understory intercrops. RTAs exhibited the most efficient Ca and Mg cycling, limiting their losses through litterfall. These results demonstrates that intercropping perennial cash crops with rubber could effectively increase biomass productivity, accumulation, turnover rate, and accompanying nutrient deposition. Constructing multispecies rubber agroforestry is an environmentally friendly management strategy to improve the ecosystem nutrient cycling flexibility and soil fertility restoration and thus ecosystem services of rubber plantations.