Dissolved organic matter driven changes in minerals and organic-mineral interactions during paddy soil development
Final Report Abstract
During the first 3-year phase, possible changes in mineral composition as well as in production and stabilization of dissolved organic matter of paddy soils with increasing number of redox cycles, i.e., time of paddy management were studied. One of the findings was the translocation and transformation of Fe oxides. Otherwise time of paddy cultivation had no strong effect on the soils’ clay mineral assemblage, the response of redox regime and solution composition to flooding and draining, the mineralization of C, and the production of DOM. All tested characteristics, however, were considerably different from those of non-paddy soils. Therefore, we conclude that the major effect of paddy cultivation is the subjection of the parent soil to strongly reducing conditions, causing a quick major shift in the biogeochemistry. Physico-chemical soil conditions (pH, salinity) and contents of Fe oxides determine the strength of redox-driven changes in paddy soil development and affected the retention and release of organic matter. Anoxic conditions caused increasing DOC concentrations in paddy soils but caused no decrease in the mineralization rates of organic matter as compared to oxic conditions. Once the paddy-type conditions fully established, soil characteristics undergo little and slow further changes, at least in soils with small initial contents of Fe oxides. On the other hand, results clearly indicated the crucial role of Fe oxides for the differences between paddy and non-paddy soils. Considering the range of different soil types subjected to paddy management (e.g., Ali- and Acrisols, Andosols, Ferralsols, Vertisols, Fluvisols), the question raising is to what extent the parent soils, differing strongly in mineral assemblage and organic matter, direct the paddy development. One scenario could be that paddy conditions overrule within little time all original differences. The other possibility is that paddy conditions, at least partly, preserve certain properties of the parent soil. Consequently, during the 2nd 3-year research period, we analysed the influence of the original soil type (and its properties) on the course of pedogenesis when subject to regular submersion. Comparing different types of soils and their respective paddy variants, we observed that organic matter input determines whether OC is accumulated under paddy management or not. Overall, paddy management-induced changes were partly influenced by the original soil and the parent material. Main characteristics of the initial soil type were preserved and not entirely overridden by paddy management. There were clear differences in biogeochemical processes of paddy soils developing from different parent soils. Incubation studies, simulating paddy management, indicate release of Fe2+ into soil solution relative to the content of poorly crystalline Fe oxides under reducing conditions. Part of the Fe2+ re-precipitates upon re-establishment of oxic conditions, then forming into poorly crystalline Fe oxides. More crystalline Fe oxides, once dissolved, do not re-form. Most dissolved Fe2+ will be leached into the subsoils. In result, the topsoils become increasingly depleted in Fe oxides, with increasing proportion of poorly crystalline Fe oxides. The incubation study also showed that most organic matter input to topsoils is mineralized or retained and little DOC may be transported into the subsoils. That explains why reducing conditions do not establish in subsoils. The oxidative conditions cause precipitation of Fe2+ leached from the topsoils; thus, subsoils become enriched in poorly crystalline Fe oxides. The incubation studies and the results of the first 3-year phase imply that the lack of input of easily degradable organic matter to subsoils is a major factor for the development of paddy soil profiles with Fe oxide-depleted top- and Fe oxid-rich subsoils.
Publications
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(2010) Biogeochemistry of paddy soils. Geoderma 157, 1–14
Kögel-Knabner, I., Amelung, W., Cao, Z.H., Fiedler, S., Frenzel, P., Jahn, R., Kalbitz, K., Kölbl, A., Schloter, M.
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(2010) Changes in diversity and functional gene abundances of microbial communities involved in nitrogen fixation, nitrification, and denitrification in a tidal wetland versus paddy soils cultivated for different time periods. Applied Environmental Microbiology 77, 6109–6116
Bannert, A., Kleineidam, K., Wissing, L., Mueller-Niggemann, C., Vogelsang, V., Welzl, G., Cao, Z., Schloter, M.
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(2011) Organic carbon accumulation in a 2000-year chronosequence of paddy soil evolution. Catena 87, 376–385
Wissing L., Kölbl A., Vogelsang V., Fu, J.-R., Cao Z.-H., Kögel-Knabner I.
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(2013) Redox control on carbon mineralization and dissolved organic matter along a chronosequence of paddy soils. European Journal of Soil Science 64, 476–487
Hanke, A., Cerli, C., Muhr, J., Borken, W., Kalbitz, K.
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(2013) The carbon count of 2000 years of rice cultivation. Global Change Biology, 19, 1107–1113
Kalbitz, K., Kaiser, K., Fiedler, S., Kölbl, A., Amelung, W., Bräuer, T., Cao, Z., Don, A., Grootes, P., Jahn, R., Schwark, L., Vogelsang, V., Wissing, L., Kögel-Knabner, I.
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(2014) Accelerated soil formation due to paddy management on marshlands (Zhejiang Province, China). Geoderma, 228-229, 67–89
Kölbl, A., Schad, P., Jahn, R., Amelung, W., Bannert, A., Cao, Z.-H., Fiedler, S., Kalbitz, K., Lehndorff, E., Müller-Niggemann, C., Schloter, M., Schwark, L., Vogelsang, V., Wissing, L., Kögel-Knabner, I.
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(2014) Does anoxic processing of dissolved organic matter affect organic–mineral interactions in paddy soils? Geoderma 228-229, 62–66
Hanke, A., Sauerwein, M., Kaiser, K., Kalbitz, K.
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(2014) Properties, processes and ecological functions of floodplain, peatland, and paddy soils. Geoderma, 228-229, 1–4
Luster, J., Kalbitz, K., Lennartz, B., Rinklebe, J.
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(2016) Response of Vertisols, Andosols, and Alisols to paddy management. Geoderma 261, 23–25
Winkler P., Kaiser K., Kölbl A., Kühn T., Schad P., Urbanski L., Fiedler S., Lehndorff E., Kalbitz K., Utami S.R., Cao Z., Zhang G., Jahn R., Kögel-Knabner I.
