Soil organic carbon under different yerba mate management system

Yerba mate (Ilex paraguariensis St. Hil.) is a tree species native to subtropical and temperate forests in South America, with natural occurrence restricted to northeastern Paraguay, the southern states of Brazil, the northeast region of Argentina, and Uruguay. In the context of Rio Grande do Sul, the green leaves of yerba mate are one of the state's main agricultural products and an important source of income for family-based agriculture. In the state, yerba mate is cultivated in two systems: shaded and full sun. In the shaded system, yerba mate grows among larger trees that provide shade, while the full sun system consists of monoculture production, with soil covered by cover crops, temporary crops, or spontaneous vegetation growing between plants. In this research, we evaluated the stock of soil organic carbon (SOC) of yerba mate produced in these two systems. To evaluate SOC stocks, we collected soil samples from the 0–20 cm layer in 242 production areas: 169 from the full sun system and 73 from the shaded system. We determined SOC by wet digestion and used clay content to estimate soil density for C stock calculations. The values of C stocks in soils cultivated with yerba mate ranged from 26.5 to 160.5 Mg ha^-1. The shaded system presented an average SOC stock of 73 Mg ha^-1, significantly higher than the 64 Mg ha^-1 of the full sun system. The results demonstrate that the crop has a potential similar to or even higher than other forest species to promote C sequestration in the soils of Rio Grande do Sul. The adoption of the shaded system amplifies this potential. This study aligns with Sustainable Development Goals (SDGs) 12 and 13 of the 2030 Agenda.