Redox processes

Completed projects

“Changes in the mineral assemblage of paddy soils upon redox cycles”, subproject (P1) of the DFG Research group 995 “Biogeochemistry of Paddy Soil Evolution” (2008 – 2011, Project phase 1)

2000 Jahre alter Nassreisboden, Zhejiang, China

Around 11% of the world's agricultural land is used for the cultivation of rice (Oryza sativa L.). The most important cultivation system here is wet rice cultivation with periodic flooding of the fields. As a result, soils are subjected to both temporal and spatial redox fluctuations. The goal of this project is to elucidate long-term effects of wet rice cultivation on mineral transformation and soil solution composition. We hypothesize that the duration of wet rice cultivation separates sites according to their redox dynamics, which is reflected in mineral stock composition, soil solution and organic matter accumulation. The studies are conducted in the Yangtze River Delta area (Zhejiang, China) along a chronosequence of wet rice soils and non-irrigated comparison sites of the same parent material. Selected sites (100 to 2000 years of wet rice cultivation) are studied for their differences in mineral content and variability in soil properties. Characterization of mineral phases will be performed by XRD, supplemented by Mößbauer spectroscopy to characterize Fe-containing mineral phases, and wet chemical extraction methods. In addition, field experiments are carried out to measure the redox ratios and composition of the soil solution, as well as weathering experiments with test minerals over several growing cycles. By combining the results, we hope to gain a better understanding of mineral transformations in soils due to redox fluctuations.

Management: Prof. Dr. Reinhold Jahn (Soil Science, University of Halle-Wittenberg) and Prof. Dr. Sabine Fiedler
Staff: Vanessa Vogelsang

“Dissolved organic matter driven changes in minerals and organic-mineral interactions during paddy soil development“, Subproject (P1) of the DFG Research group 995 “Biogeochemistry of Paddy Soil Evolution” (2012 – 2015, Project phase 2)

Preliminary studies indicate that development and biogeochemistry of wet rice soils depend on the parent material, i.e. the original soil type. The proposed research project aims at the changes in mineral content and mineral-associated organic matter caused by redox morphosis. For this purpose, soil samples will be subjected to a sequence of redox cycles. The aim is to experimentally investigate formation and development of wet rice soils in the laboratory. The selected soil types will exhibit a wide range of properties as well as different stages of development into wet rice soils. We hypothesize that dissolved organic matter is a key factor in the redox-induced transformation to wet rice soils. It serves as an electron donor and interacts with metal ions and minerals. The magnitude of the effects should depend on mineral content and organic matter (and their interactions) of the parent soil. Experimental wet rice soil formation will be followed by studies of soil solution, carbon redistribution (using 13C-labeled rice straw), biomarkers (sugars, amino acids, fatty acids, lignin), and minerals (including the redox state of Fe). Analysis of organic matter as well as minerals will also be done using EXAFS and XPS; for Fe-containing minerals, we plan to use Mössbauer spectroscopy. Our concept of an experimental pedology promises to comprehensively improve our understanding of the main factors in the formation and development of wet rice soils.

Management: Dr. Klaus Kaiser, Prof. Dr. Reinhold Jahn, Prof. Dr. Sabine Fiedler
Staff: Pauline Geier (Soil Science, University of Halle-Wittenberg)
Cooperation: Prof. Dr. Karsten Kalbitz (Earth Surface Sciences, University of Amsterdam)