Assessments on the Potential Use of Rhyolite Filler as a Soil Remineralizer in Agroecological Practices in the Fourth Colony of Italian Immigration, Rio Grande do Sul, Brazil

Abstract

This study examined the application of rhyolite filler in agroecological farming systems in the Fourth Colony of Italian Immigration (Quarta Colônia de Imigração Italiana), Rio Grande do Sul, Brazil. The aim was to explore sustainable alternatives to synthetic fertilizers in line with organic agriculture principles. The region’s designation as the Quarta Colônia UNESCO Global Geopark reinforces the relevance of this initiative. The research involved petrographic characterization, incubation experiments, and chemical analyses of rhyolite samples. Incubation tests with pigeon pea and elephant grass assessed combinations of rock filler and poultry litter. The results showed that rhyolite filler supported plant growth, especially with poultry litter, which supplies nitrogen and microorganisms that accelerate mineral weathering. Petrographic observations indicated that elephant grass promoted stronger mineral alteration, likely due to its dense fibrous roots and substrate interaction. Chemical analyses confirmed the rhyolite’s quartz content and trace elements remain within safety limits defined by Brazilian legislation on soil remineralizers. The K2O content and the base sum (CaO, MgO, and K2O) also complied with minimum legal requirements. Beyond mineralogical and chemical aspects, the study emphasized the economic feasibility of using locally sourced rock fillers, offering lower costs than synthetic fertilizers and supporting sustainable, resilient agroecological systems.