Journal
GLOBAL CHANGE BIOLOGY
Volume 20, Issue 6, Pages 1968-1978Publisher
WILEY
DOI: 10.1111/gcb.12468
Keywords
benzene-polycarboxylic acids; black carbon; chronosequence; crop residue combustion; mean residence time
Funding
- German Research Foundation (DFG) [FOR 995, AM 134]
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Rice straw burning has accompanied paddy management for millennia, introducing black carbon (BC) into soil as the residue of incomplete combustion. This study examined the contribution of BC to soil organic matter and the rate at which it accumulates in paddy soils as a result of prolonged paddy management. Soil depth profiles were sampled along a chronosequence of 0-2000years of rice-wheat rotation systems and adjacent non-paddy systems (50-700years) in the Bay of Hangzhou (Zhejiang province, China). The soil BC content and its degree of condensation were assessed using benzene-polycarboxylic acids (BPCAs) as geochemical markers. The results showed that despite regular long term BC input, BC only contributed 7-11% of total soil organic carbon (SOC) in the topsoil horizons. Nevertheless, along with SOC, paddy soils accumulated BC with increasing duration of management until 297years to reach a steady-state of 13tBCha(-1). This was 1.8 times more than in non-paddy soils. The fate of BC in paddy soils (0-1m) could be modeled revealing an average annual input of 44kgha(-1)yr(-1), and a mean residence time of 303years. The subsoils contributed at least 50% to overall BC stocks, which likely derived from periods prior to land embankment and episodic burial of ancient topsoil, as also indicated by BPCA pattern changes. We conclude that there is a significant but limited accumulation of C in charred forms upon prolonged paddy management. The final contribution of BC to total SOC in paddy soils was similar to that in other aerobic ecosystems of the world.
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