Changes in the mineral composition of paddy soils upon redox cycles

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The study objective is to elucidate the processes of mineral transformation and changes in the composition of the soil solution as related to redox conditions. It is assumed that the duration of rice cultivation separates soils of comparable parent materials according to the redox status (memory effect), which is reflected by the mineral assemblage, the chemical composition of soil solution, and the carbon storage. The planned work includes field measurements of redox conditions, analyses of soil solutions and weathering experiments with test minerals along a chronosequence of recent (50 to 1000 years after dyking) paddy soils in comparison with non-paddy soils. Recent, buried ancient (up to 3000 years) and prehistoric paddy soils (up to 6000 years old) and their non-irrigated/cultivated counterparts will be analysed for differences in the mineral assemblage. Batch experiments will provide additional information on effects of redox conditions on test minerals and composition of the soil solution. The results will be evaluated using the program code PHREEQC for speciation of solutes and possible dissolution and precipitation of mineral phases and will provide a better understanding of mineral transformation as affected by redox conditions.