Shaded Yerba Mate as a Strategy for Restoring Soil Organic Carbon Stocks

Soil organic matter (SOM) is considered the key indicator of soil quality. Increasing carbon stocks in agricultural soils is also a fundamental strategy for addressing climate change. In this context, yerba mate emerges as a species with decarbonizing potential.

This study aimed to evaluate SOM stocks in two yerba mate production systems, compared with reference systems. The research was conducted in Ilópolis, Rio Grande do Sul, Brazil. Using volumetric rings, undisturbed soil samples were collected under full‑sun and shaded yerba mate, as well as two reference systems: a native forest and a conventionally tilled cropland. Samples were taken from the 0–5, 5–10, 10–20, and 20–30 cm layers. For each layer, soil bulk density, C stock, and SOM C:N ratio were determined, along with total C stock from 0–30 cm.

Total C stock was calculated using an equivalent soil mass approach, with the native forest used as the reference system to standardize differences in bulk density. Bulk density was highest in the cropland and full‑sun system, and lowest under native forest, while the shaded system showed intermediate values. The SOM C:N ratio was highest in the native forest soil, indicating more labile organic matter; the other treatments did not differ. Total SOM stock was significantly higher in the native forest, nearly 80 Mg ha⁻¹, and lowest in the full‑sun and cropland systems, around 40 Mg ha⁻¹. The shaded system surpassed both, with 55.8 Mg ha⁻¹, demonstrating its capacity to partially restore original SOC levels.