The carbon count of 2000 years of rice cultivation

Abstract

More than 50% of the world's population feeds on rice. Soils used for rice production are mostly managed under submerged conditions (paddy soils). This management, which favors carbon sequestration, potentially decouples surface from subsurface carbon cycling. The objective of this study was to elucidate the long-term rates of carbon accrual in surface and subsurface soil horizons relative to those of soils under nonpaddy management. We assessed changes in total soil organic as well as of inorganic carbon stocks along a 2000-year chronosequence of soils under paddy and adjacent nonpaddy management in the Yangtze delta, China. The initial organic carbon accumulation phase lasts much longer and is more intensive than previously assumed, e.g., by the Intergovernmental Panel on Climate Change (IPCC). Paddy topsoils accumulated 170-178 kg organic carbon ha(-1) a(-1) in the first 300 years; subsoils lost 29-84 kg organic carbon ha(-1) a(-1) during this period of time. Subsoil carbon losses were largest during the first 50 years after land embankment and again large beyond 700 years of cultivation, due to inorganic carbonate weathering and the lack of organic carbon replenishment. Carbon losses in subsoils may therefore offset soil carbon gains or losses in the surface soils. We strongly recommend including subsoils into global carbon accounting schemes, particularly for paddy fields.

Rice methylmercury exposure and mitigation: A comprehensive review

“…During field preparation, both burned and unburned residues are incorporated into paddy soil as mulch, depending on the type of cropping system (e.g., rice-rice, rice-wheat), resulting in higher soil C content (Kalbitz et al, 2013). Over an annual cycle, highest concentrations of pore water acetate and associated MeHg production rates were observed during winter post-harvest, which likely reflected post-harvest litter decay (Marvin-DiPasquale et al, in press; Windham-Myers et al in press, a).…”

Carbon release from rice roots under paddy rice and maize–paddy rice cropping

“…Organic carbon (C) stocks of paddy soils are often elevated in comparison to other soils (Cai, 1997;Pan et al, 2003Pan et al, , 2009, particularly in topsoils (Kalbitz et al, 2013). However, many paddy rice systems are currently under change.…”

Response of Vertisols, Andosols, and Alisols to paddy management

“…Thus, frequent inundation leads to reduced rates of OM decomposition (Sahrawat, 2004(Sahrawat, , 2005, which may result in increases in OM storage (Cheng et al, 2009;Kögel-Knabner et al, 2010). Most OM storage under paddy management is restricted to the puddled layer Chen et al, 2011;Kalbitz et al, 2013;Roth et al, 2011;Wissing et al, 2011). The paddy-specific dense plow pan prevents OM from entering deeper soil layers, likely due to less deep rooting and diminished vertical water fluxes Lennartz, 2006, 2007;Kalbitz et al, 2013).…”

“…Most OM storage under paddy management is restricted to the puddled layer Chen et al, 2011;Kalbitz et al, 2013;Roth et al, 2011;Wissing et al, 2011). The paddy-specific dense plow pan prevents OM from entering deeper soil layers, likely due to less deep rooting and diminished vertical water fluxes Lennartz, 2006, 2007;Kalbitz et al, 2013). Thus, the dense plow pan decouples topsoil from subsoil OM cycling (Kalbitz et al, 2013;Wissing et al, 2011).…”

“…The paddy-specific dense plow pan prevents OM from entering deeper soil layers, likely due to less deep rooting and diminished vertical water fluxes Lennartz, 2006, 2007;Kalbitz et al, 2013). Thus, the dense plow pan decouples topsoil from subsoil OM cycling (Kalbitz et al, 2013;Wissing et al, 2011). In addition to the numerous publications that show OM accumulation in paddy soils, Kirk (2004) and Kögel-Knabner et al (2010) reviewed studies that are not in line with that generally accepted theory.…”