Thermodegradation of organic matter in soils of different mineral composition in Brazil

• Published in: Geoderma Regional 2024-06, Vol.37, p.e00798, Article e00798
• Main Authors: dos Santos, Sara Ramos, Costa, Liovando Marciano da, Souza, Carolina Malala Martins, Leal, Greice Pereira, Mello, Danilo Cesar de, Silva, Wilson Tadeu Lopes da, Camêlo, Danilo de Lima, Schaefer, Carlos Ernesto Gonçalves Reynaud
• Format: Article
• Language: English
• Subjects: Atlantic forest; Brazilian savanna; Chemical stability; Dry Forest; Humification; Soil organic matter
• ISSN: 2352-0094; 2352-0094
• DOI: 10.1016/j.geodrs.2024.e00798

Thermodegradation is an analytical tool that quantifies the loss of organic carbon under increasing temperatures. The degradation process is related to chemical functions and provides data on the stability of soil organic matter (SOM). There needs to be more information about SOM stability in different Brazilian ecosystems. This study aimed to evaluate SOM stability under three tropical environments: Dry Forest, Brazilian Savanna, and Atlantic Forest. Thus, we related thermal stability to soil mineral composition and SOM quality and quantity. We analyzed samples of the surface horizon of four illitic soil profiles sampled in Dry Forest (P1 to P4), three soil profiles in Cerrado (Brazilian Savanna), with predominant 2:1 clay (P5), iron oxide (P6), and gibbsite (P7), and a kaolinite profile from Atlantic Forest (Rainforest) (P8). Mineralogical, chemical, and physical analyses of the soils were studied to better comprehend soils' behavior under thermodegradation. The thermic treatment was performed by heating air-dried fine earth (ADFE) samples at 100, 200, 300, 400, and 500 °C for 2 h. The results were submitted to sigmoidal regression with four points and presented a good curve fit (r2 > 0.99). Dry Forest soils with the most humified SOM presented greater resistance to loss of SOM by the thermic process. However, P7 (gibbsitic clayey soil) stood out and was the most resistant to thermodegradation. P4 was the sandiest soil and showed the curve most affected by the thermal process, indicating the importance of clay content to SOM stability. The results suggest that the TOC (content and quality), calcium content, and clay (content and type) play essential roles in determining the thermostability of SOM in different ecosystems. •Thermodegradation can indicate soils with greater and smaller resistance to C loss.•The sigmoidal model (four points) adequately represents C loss in thermal analysis.•Clay content and TOC (content and quality) are factors that affect the curves.•OM–mineral stability is gibbsite > illite > montmorillonite = hematite > kaolinite.