14C AMS as a tracer to study carbon dynamics resulting from paddy management under different climatic conditions in different soil types

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Phase 1 of Research Unit 995, “Biogeochemistry of paddy soil evolution”, showed a very fast replacement of carbon, originating from the parent material (estuarine sediments near Cixi, Zhejiang Province, China), with organic carbon derived from the recent atmosphere in paddy top soils; carbon replacement in non-paddy top soils was slower. Increasing 14C concentrations in the subsoil at constant or decreasing organic carbon (OC) documented the replacement of original estuarine OC by transport from above in both paddies and non-paddies, though at a slower pace under paddies. We hypothesize that measured concentration profiles in OC and 14C, found in paddy soils, represent snapshots of the dynamic balance between import of young carbon from above, its mineral stabilisation, and mineralisation and leaching. These carbon fluxes, in turn, depend on the input of fresh photosynthate, rainfall/irrigation, temperature, permeability of the plough pan (if any), soil microbes, soil mineral composition, and paddy management. In the second phase we will focus on different parent materials and correlated climatic regions, resulting in different main soil types (Acrisols/Ferralsols, Silandic Andosols, Aluandic Andosols, and Vertisols), to separate the influence of soil type and climate from that of management. Considering the rapid OC replacement at Cixi, a short Indonesian chronosequence from the Simo village area, where the onset of paddy cultivation is defined by the construction of irrigation canals in the years 1908, 1965 and 2006, is of special importance.