Qualidade física de solo com caráter coeso em resposta à adição de carvões hidrotérmico e pirolítico

Abstract

Soils treated with biochars, such as hydrochar and pyrochar, show improvements in physical quality indicators and are therefore recognized as soil conditioners. In this context, it is relevant to evaluate the effects of incorporating these conditioners into soils with physical constraints, such as those exhibiting a cohesive character. This study was based on the hypotheses that: (i) the application of cashew bagasse hydrochar improves the physical quality of cohesive soils due to silicon adsorption, leading to reduced cohesion and improved soil structure; (ii) there is an optimal hydrochar dose to maximize soil physical quality; and (iii) hydrochar performs better than biochar derived from the same feedstock. The objectives were to evaluate soil physical quality using indicators sensitive to structural changes, to identify the most efficient hydrochar dose, and to compare, through a joint analysis of experiments, the effects of hydrochar and biochar applied under the same experimental conditions. Disturbed soil samples were collected from the Bt1 horizon, with cohesive character, of an Argissolo Amarelo Eutrocoeso típico, in Fortaleza, Ceará State, Brazil. Test specimens were prepared using air-dried fine earth and increasing hydrochar doses (0, 5, 10, 20, 40, and 80 Mg ha-1). The samples were subjected to ten wetting–drying cycles to induce the manifestation of the cohesive character. Traditional physical and rheometric properties were evaluated. The experiment followed a completely randomized design. Data were analyzed using univariate and multivariate statistics, regression, and correlation analyses, employing the SAS® OnDemand for Academics platform. Compared with the control treatment, the highest hydrochar dose increased silicon adsorption capacity (+30%), clay flocculation degree (+18.8%), microporosity (+8.8%), and air permeability (+25.7%). In contrast, saturated hydraulic conductivity decreased (–23.2%), particularly at higher doses, indicating partial pore filling. Penetration resistance (–12.1%) and aggregate tensile strength (–38.7%) were also reduced, indicating mitigation of physical constraints associated with the cohesive character. It was concluded that the application of cashew bagasse hydrochar promotes silicon adsorption and reduces soil cohesion; that doses between 20 and 40 Mg ha-1 are the most effective for improving soil physical quality; and that hydrochar and biochar exhibit similar effects, with both biochars being effective soil conditioners.