Sustainable Soil Amendment with Basalt Powder: Unveiling Integrated Soil–Plant Responses in Ilex paraguariensis Cultivation

As a sustainable alternative to conventional fertilizers, rock dusting is an emerging agroecological strategy to improve soil health and nutrient availability. This study aimed to quantify the effects of basalt powder (BP) application on the chemical attributes of a Ferralsol and the morphological responses of young Ilex paraguariensis (yerba mate) plants. The experiment was conducted in a randomized block design with five BP doses (0, 3.8, 7.6, 15.2, and 30.4 Mg ha−1), where resulting soil and plant parameters were statistically analyzed. Results demonstrated that BP significantly increased available calcium, magnesium, and silicon in the soil (p ≤ 0.05) without altering pH or potassium levels. This soil enrichment directly correlated with a significant increase in the number of leaves per plant (p ≤ 0.01), which was strongly associated with soil Mg2+ (r = 0.73) and Si (r = 0.40). However, no significant effects were observed on plant height or stem diameter. We conclude that basalt powder acts as an effective slow-release source of Ca, Mg, and Si, primarily stimulating leaf development rather than immediate plant structural growth. This finding is consistent with the gradual nutrient release from silicate rocks and suggests that BP is a viable tool for enhancing soil fertility in yerba mate systems, although long-term evaluation is essential to understand its full agronomic potential.