Geological viability and nutrient availability of andesitic basalt rock powder as a soil remineralizer

Abstract

Brazilian soils are prone to a gradual decline in fertility due to intensive agricultural activity combined with the natural process of weathering. However, the use of conventional fertilizers results in a series of negative environmental impacts and limited access for smallholder farmers, as these products are typically imported. Over the past two decades, the development and improvement of techniques aimed at meeting crop nutritional needs with lower environmental impact have intensified significantly. Soil remineralization consists of supplying macro- and micronutrients through the addition of ground rock from specific lithologies. Law No. 12,890/2013 marked a milestone in the dissemination of this technique in Brazil by including remineralizers in the category of agricultural inputs. This law was later complemented by Normative Instruction No. 5/2016 from the Ministry of Agriculture, Livestock, and Supply, which established the technical criteria required for a rock to be commercialized as a soil remineralizer. The present study aimed to assess the geological viability and efficiency of ground andesitic basalt, occurring in southern Brazil, for use as a soil remineralizer. The methodology included mineralogical and geochemical characterizations, along with a leaching test to evaluate nutrient availability. Geochemical analysis showed that the lithology contains more than 15% of total base-forming oxides (K₂O, MgO, and CaO), with K₂O exceeding 1%, and lacks significant concentrations of potentially toxic elements (As, Cd, Hg, and Pb), thus complying with current legislation. Likewise, the leaching test using a 2% citric acid solution demonstrated the release of 36.25 mg/L of Ca, 24.95 mg/L of Mg, and 12.06 mg/L of K, confirming the nutrient availability under simulated acidic soil conditions. These findings confirm the geological viability of this lithology for use as a soil remineralizer. However, further field studies are recommended, as the current results are based exclusively on laboratory-scale experiments.