Crushed fines from basic rocks of the Serra Geral Group as the sole substrate for assessing bioweathering and nutrient release in elephant grass cultivation (Cenchrus purpureus)

Tropical agriculture, generally developed on acid and leached soils, is highly dependent on soluble synthetic fertilizers (SSF), highlighting the need for local, economically viable, and more sustainable alternatives. Although intensive agriculture has increased global productivity through the use of these inputs, inadequate replacement of secondary nutrients and micronutrients has contributed to the progressive depletion of soil nutrients. In this context, agrogeology, particularly through the use of silicate agrominerals (SiA), emerges as a promising approach to assist developing countries in reducing their dependence on imported SSF by promoting the use of regional geological resources, such as crusher fines (CF) generated in the aggregate production chain for civil construction. This study evaluated nutrient release and plant uptake from CF derived from basic rocks of the Serra Geral Group (basalt and diabase), using an agronomic trial in which CF were used as the sole substrate, without soil addition. Elephant grass (cultivar BRS Kurumi) was grown with and without organic matter (OM) over 182 days in a greenhouse experiment arranged in a 2 × 2 factorial design, in addition to a control treatment.Reductions in Ca, Mg, K, and Si contents were observed in CF from plant treatments, more pronounced in the presence of OM, and were accompanied by substantial increases in nutrient uptake by elephant grass (up to 6.5-fold for basalt and 6-fold for diabase with OM) and in shoot dry matter (5.1 to 5.8-fold). The higher proportion of fine fractions in basalt CF favored nutrient release compared to diabase.The results indicate that bioweathering, driven by plant–OM interactions, intensified mineral dissolution and short-term release of K, Ca, Mg, Fe, and Si over months, supporting the use of CF from the studied lithologies as silicate agrominerals. The integration of SiA, plants, and OM increases biological activity, intensifies mineral dissolution in CF, and enhances agronomic efficiency, representing a viable strategy to reduce dependence on SSF in tropical agricultural systems.