Pedotransfer Functions in the Assessment of Fragile Mountainous Areas: Carbon and Nitrogen Stocks in Mountains in Southeastern Brazil

Objective: This study aimed to obtain the Bd of organic constitution horizons through PTFs and evaluate the C and N stocks of different soil classes found in the upper part of the INP. Theoretical framework: The evaluation of bulk density (Bd) depends on the method used to obtain the sample and presents great spatial variability, especially in mountainous regions such as the upper part of Itatiaia National Park (INP), Brazil. Techniques can be used for this purpose, including those of pedotransfer functions (PTFs) allowing the quantification of nutrients such as C and N in soils. Methodology: The research was conducted within the Itatiaia National Park (INP), situated in the Mantiqueira Mountains of southeastern Brazil. Soil samples were collected from the upper portion of the INP, specifically targeting soil profiles containing hystic horizons (O or H). The study employed pedotransfer functions (PTFs) established by Beutler et al. (2017) to estimate the soil bulk density (Bd) of organic horizons. Based on these assessments, stocks of carbon (C) and nitrogen (N) were calculated. The standard depth for these calculations was 30 cm. In total, 47 profiles were selected, 26 of which belonged to the order Histosols, 15 to Cambisols, and 6 Leptosols & Regosols. Results and conclusion: In general, a high C content, between 5 and 15 g kg-1, and N contents greater than 1.0 g kg-1 were observed. For Bd an increase in depth occurred, with values close to 0.50 Mg m-3 in the superficial horizons and > 0.75 Mg m-3 in depths greater than 30 cm. The area occupied by soil profiles presenting hystic horizons corresponds to 16403.69 ha (hectares) with 315645.7 Mg of C and 20043.0 Mg of N. Of this total, 10254.44 ha were Cambisols that store approximately 205282.1 Mg of C and 13121.8 Mg of N. Histosols occupied an area of 4148.38 ha and stored 90698.4 Mg of C and 5576.0 Mg of N. The area occupied by Leptosols & Regosols was 1347.74 ha and they stored 19665.1 Mg of C and 1345.1 Mg of N. For the Cambisols, the average values of C and N stocks were lower than those quantified in the Histosols, but considering the area occupied, the total C stock was more than twice the amount quantified in the Histosols. Research implications: Soils with organic horizons complicate Bd determination due to costly and unrepresentative collection methods. Additionally, converting soil masses to volume for nutrient stock measurements (e.g., C and N) is problematic. Due to limited accessibility in certain areas, obtaining undisturbed soil samples for evaluation can be challenging. In such cases, pedotransfer functions (PTFs) play a crucial role in assessing and modeling soil phenomena. Indirect quantification of Bd using PTFs has become essential for addressing these issues. Originality/value: This study utilizes pedotransfer functions (PTFs) to estimate soil bulk density (Bd) and, consequently, nutrient stocks in fragile mountainous soils, enabling monitoring of these environments.