Assessing the morphological, physicochemical, and mineralogical properties of black soils and ferralsols and identification of potential risk of degradations along a climotoposequence in Foumbot, West Cameroon

Abstract

Foumbot in Cameroon is renowned for its fertile soils, which serves as a food basket for the region. However, these soils are currently under threat due to climate change and overutilization. As such, there is a need to better understand their properties, variability and identify the degradation risks to improve their management and conservation. To address this gap, soil profiles formed under volcanic deposits were sampled at three distinct altitudes: 1156 m (highland), 1075 m (middle land), and 974 m (lowland), representing tropical highland, transitioning tropical highland, and tropical forest climates, respectively. Physical and chemical analyses, X-ray diffraction (XRD) and Fourier-Transform Infrared (FTIR) techniques, were conducted to determine the variability of soil morphology, physical and chemical properties, and mineralogy as well as soil classification under climotoposequence. The findings reveal that pedon 1 in the highland was dark in colors (2.5Y and 10YR), slightly acidic to neutral and exhibited the highest organic carbon content (6.8 %) in the surface horizon. In contrast, the middle land, showed a slightly acidic profile (pedon 2) characterized by a darker surface horizon (10YR) with a yellowish subsoil (7.5YR) and lower organic content (4.1 %) in surface horizon compared to pedon 1. Finally, the lowland profile (pedon 3), displayed more acidic conditions and the lowest soil organic carbon content (2.5 %) in surface horizon compared to pedon 1 and pedon 2. A trend of decreasing Alo + ½Feo and Alp/Alo alongside increasing clay content was observed with decreasing altitude. Mineralogical analysis revealed a transition from short-range ordered minerals (allophane and ferrihydrite) in highland soils to poor crystalline kaolinite dominance in the middle land and well crystalline kaolinite in lowland. Additionally, bulk density increased with decreasing altitude. According to the WRB classification, Pedon 1 was classified as Mollic Vytric Silandic Andosol (Loamic, Eutrosilic, Humic), Pedon 2 as Dystric Xanthic Andic Ferralsol (Clayic, Humic), and Pedon 3 as Umbric Rhodic Ferralsol (Clayic, Humic). Andosol was identified as black soil and presents greater potential for agricultural productivity compared to the two other pedons. Since andosols are situated at the top of the hill, possess structural weaknesses (granular structure), and are subjected to intensive cultivation, they pose a higher potential risk of degradation when farming is practiced compared to the other two pedons. This study highlights the significant influence of pedogenetic factors on the soil properties and mineral composition and reveals the urgent need of adopting new soils sustainable management strategies to protect black soils in the Foumbot region of Cameroon.