The turnover of organic carbon in subsoils. Part 2. Modelling carbon turnover

Abstract

A new model, RothPC-1, is described for the turnover of organic C in the top metre of soil. RothPC-1 is a version of RothC-26.3, an earlier model for the turnover of C in topsoils. In RothPC-1 two extra parameters are used to model turnover in the top metre of soil: one, p, which moves organic C down the profile by an advective process, and the other, s, which slows decomposition with depth. RothPC-1 is parameterized and tested using measurements (described in Part 1, this issue) of total organic C and radiocarbon on soil profiles from the Rothamsted long-term field experiments, collected over a period of more than 100 years. RothPC-1 gives fits to measurements of organic C and radiocarbon in the 0-23, 23-46, 46-69 and 69-92 cm layers of soil that are almost all within (or close to) measurement error in two areas of regenerating woodland (Geescroft and Broadbalk Wildernesses) and an area of cultivated land from the Broadbalk Continuous Wheat Experiment. The fits to old grassland (the Park Grass Experiment) are less close. Two other sites that provide the requisite pre-and post-bomb data are also fitted; a prairie Chernozem from Russia and an annual grassland from California. Roth-PC-1 gives a close fit to measurements of organic C and radiocarbon down the Chernozem profile, provided that allowance is made for soil age; with the annual grassland the fit is acceptable in the upper part of the profile, but not in the clay-rich Bt horizon below. Calculations suggest that treating the top metre of soil as a homogeneous unit will greatly overestimate the effects of global warming in accelerating the decomposition of soil C and hence on the enhanced release of CO 2 from soil organic matter; more realistic estimates will be obtained from multi-layer models such as RothPC-1.

The effect of vertically resolved soil biogeochemistry and alternate soil C and N models on C dynamics of CLM4

“…These factors could include: (1) pore-scale anoxia beyond the bulk anoxia limitation we apply here; (2) a strong control by the microbial community and the possible priming effects that may result from microbial population dynamics and lead to lesser microbial activity at depth; (3) other stabilization mechanisms such as SOM-mineral surface interactions, which may become more important with depth due to a smaller quantity of SOM relative to the total amount of mineral surface area. A similar explicit depth dependence to turnover time was found by Jenkinson and Coleman (2008). Future work to better understand the processes that control the vertical profiles of SOM turnover and stabilization is needed.…”

“…A major uncertainty is created by the fact that we do not have information on actual soil depths globally, and so we assume that soil carbon and nitrogen cycling can take place to the 3.8 m depth everywhere. A similar vertical distribution of soil biogeochemical cycling was introduced into the RothC carbon model (Jenkinson and Coleman, 2008;. We follow a conceptually similar approach here, although an important difference between RothC and the one described here is that the RothC model assumes layers of defined thickness and discrete processes based on those layer thicknesses; here we define a model that is independent of vertical resolution and thus can be compared more easily with observation-based estimates of, e.g., soil mixing rates.…”

“…Riley et al (2011) Lastly, a possible explicit depth dependence, r z , can be applied to soil C turnover times to account for processes other than temperature, moisture, and anoxia that can limit decomposition. This depth dependence of decomposition was shown by Jenkinson and Coleman (2008) to be an important term in fitting total C and 14 C profiles, and implies that unresolved processes, such as priming effects, microscale anoxia, soil mineral surface and/or aggregate stabilization may be important in controlling the fate of carbon at depth. Here, we include these unresolved depth controls via an exponential decrease in the soil turnover time with depth:…”

A vertical representation of soil carbon in the JULES land surface scheme (vn4.3_permafrost) with a focus on permafrost regions

“…5), by including an extra reduction of respiration with depth, based on Jenkinson and Coleman (2008) and Koven et al (2013). This accounts for factors that are currently missing in the model such as priming 962 E. J.…”

Life Cycle Assessment (LCA) of Light-Weight Eco-composites

“…To date, the major process-oriented models for GHG emissions from agricultural systems include DNDC , Daycent which was developed based on the Century model (Kelly et al, 1997), Roth-C 26.3 (Coleman et al, 1997) and its new version RothPC-1 (Jenkinson and Coleman, 2008), Sundial (Bradbury et al, 1993, Goulding et al, 1998 expert N (Kaharabata et al, 2003) and Ceres (Gabrielle et al, 2006). …”