Estoque de carbono e fertilidade de tecnossolos originados de rejeitos da mineração de scheelita no semiárido brasileiro

Abstract

Studying technosols is essential to understand their potential for agricultural production, reclaim degraded areas, and sequester carbon. In the semi-arid region of Northeast Brazil, the largest scheelite mine in South America is located, and waste from this activity has been accumulating since the 1940s, impacting environmental quality. Although technosols originating from mining waste are studied globally, information on the fertility and organic carbon stock of these soils is scarce in Brazil, especially in semi-arid regions. Therefore, this study aims to assess the carbon stock and fertility of technosols constructed 40 years ago from scheelite mining waste in the Brazilian semi-arid, with the purpose of evaluating their potential for agricultural use and carbon sequestration. Forty composite samples were collected from the surface horizons (0-30 cm) of technosols constructed from waste at the Brejuí Mine, located in the municipality of Currais Novos, in the semi-arid region of the state of Rio Grande do Norte. The average soil density was 1.38 kg dm-3, potentially not negatively impacting the physico-hydraulic properties of the technosols. The average pH in water and KCl was 8.53 and 8.07, respectively, with a mean ΔpH of -0.47. The alkalinity in technosols, due to carbonates in tactites and marbles (materials forming the waste), may restrict plant growth by causing nutritional imbalances and micronutrient deficiencies. The average available concentrations of P (2.73 mg kg-1) and K (0.14 cmolc kg-1) are limitations for agricultural activity, requiring strategies to increase these nutrients to improve agricultural viability. The average organic carbon concentration in technosols was 24.11 g kg⁻¹, more than double the average observed in Caatinga soils, which is typically around 9.3 g kg⁻¹. The technosols derived from scheelite mining achieved carbon stocks of up to 222.93 Mg ha-1, surpassing Vertisols (60.08 Mg ha-1) by over three times and more than doubling the national average (99.39 Mg ha-1), highlighting their potential for carbon sequestration in the semi-arid region. This study, given the scarcity of information on technosols derived from mining in Brazilian semi-arid environments, contributes not only to the scientific community but also to policy-makers, emphasizing the importance of efficient mining waste management in the recovery of degraded areas, sustainable agricultural production, and carbon sequestration, crucial for mitigating climate change.