Project Details
Projekt
Deciphering mineral inventories and their controls on soil organic matter cycling in tropical Vertisols: Key to sustainable soil management
Subject Area
Soil Sciences
Term
since 2025
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 565570285
Tropical Vertisols are intensively used for agriculture and thus of great economic relevance in many African countries. Despite their high contents in expandable phyllosilicate clays (smectites) and pedogenic iron (Fe) oxides, both of which possess high sorption capacities for organic compounds, they are generally carbon poor and can degrade rapidly. The underlying causes as well as possible avenues for sustainable soil amelioration remain elusive, partially due to inconclusive results obtained in previous studies. In an explorative field study in northern Cameroon, we showed that tropical Vertisols can vary strongly in their content and composition of phyllosilicate clays and Fe oxides and identified parent material as well as duration and intensity of annual soil inundation as plausible factors explaining the mineralogical variability. In the present project, we systematically disentangle the effects of either factor on the properties of secondary mineral assemblages and mineral-associated organic matter (MAOM). We will sample Vertisols in four geologically distinct regions of northern Cameroon and perform in-depth analyses of their physicochemical and mineralogical characteristics. In addition to wet-chemical extractions, quantitative phase analysis using X-ray diffractometry as well as surface area, porosity and electron microscopy analyses, 57Fe Mössbauer spectroscopy and Fe K-edge X-ray absorption spectroscopy will inform about differences in soil Fe speciation. MAOM will be quantified by density fractionation and its molecular characteristics revealed by biomarker analyses, 13C nuclear magnetic resonance and photoelectron spectroscopy. Sorptive properties of the Vertisols towards dissolved organic matter will be studied by adsorption-desorption experiments using high-resolution mass spectrometry to determine the effects of mineralogy on sorptive fractionation patterns. The vulnerability of MAOM towards microbial degradation as well as the potential for MAOM neoformation and their link to redox-induced mineral transformations will be studied during oxic and anoxic incubations with different amounts of 13C-labelled sorghum straw and mineral N fertiliser. Multivariate statistical analyses will reveal important links between mineralogical inventories and their dynamics and MAOM contents, composition, stability, and potential for neoformation. The proposed project represents a hitherto unique approach to explore the coupled dynamics of mineral and organic matter in redox-affected tropical Vertisols. The gained insights will support devising sustainable management strategies for Vertisols in underprivileged African regions experiencing a steep population increase.
DFG Programme
Research Grants
International Connection
Cameroon
Co-Investigator
Professor Dr. Christian Mikutta
International Co-Applicants
Dieudonné Djackba Danra, Ph.D.; Professor Dr. Mazi Sanda
