Soil carbon-to-nitrogen ratios for organic-matter balances.
Source:R/datasets_balances.R
soil_cn_ratios.RdSoil carbon-to-nitrogen ratios used to convert a soil organic carbon stock change into net nitrogen mineralization (when carbon is lost) or net nitrogen sequestration (when carbon accumulates), by cropland class and management system.
Format
A tibble with columns:
- cropland_class
Land class:
"Cropland"or"NonCropland".- management
Management system:
"Conventional"or"Organic". Only the"Conventional"rows are selectable by this package.build_carbon_balance()has no management dimension – it is a global gridded balance – so an argument for this column could only be set world-wide, and "run the whole world as organic" is not a run anyone should perform. The"Organic"rows therefore ship as reference values for downstream consumers, not as inputs this package can be asked to use (issue 809).- cn_ratio
Soil organic-matter carbon-to-nitrogen ratio.
- cn_mineralization
Carbon-to-nitrogen ratio applied when soil organic carbon is mineralized (net carbon loss).
- cn_sequestration
Carbon-to-nitrogen ratio applied when soil organic carbon is sequestered (net carbon gain).
Source
Expert parameterisation with a documented rationale and no
citation. Traced through the coefficient workbook of the earlier
regional historical reconstruction the values come from, whose C:N sheet
has no source column and no notes column, as does the packaged
inst/extdata/balances/soil_cn_ratios.csv:
The bulk ratios (
cn_ratio10 cropland, 15 non-cropland) enter the workbook on 2025-03-14, in a sheet holding onlyCropland_classandCN_ratio. The workbook's earliest tracked version (2021-02-19) has no such sheet at all.The asymmetry – management stratification plus
cn_mineralizationandcn_sequestration– is added on 2026-03-26, together with an N-limitation on SOC sequestration.
The rationale recorded with the values is: a lower ratio on mineralization for the microbial-biomass and labile pools that are preferentially decomposed, a higher one on sequestration for stable humus formation, and organic cropland sequestering at 13 against 11 conventional for the larger stable-humus fraction of manure- and compost-derived carbon. No citation is attached to any of the values.
One published anchor exists nearby and is worth knowing: the source's
methods cite Cleveland & Liptzin (2007),
doi:10.1007/s10533-007-9132-0
, for a soil microbial-biomass C:N of
roughly 8-13, and the cropland cn_mineralization values (8 and
9) fall inside it. It is cited there for a different parameter, and it
is not offered here as the source of these numbers – only as the
nearest published range they are consistent with.
This entry previously cited Coleman & Jenkinson's RothC (1996) as the
framework the values are "consistent with". That attribution has been
removed: RothC is a carbon-only model and sets no carbon-to-nitrogen
ratio at all – calculate_soc_rothc returns dpm,
rpm, bio, hum, iom and soc_total,
and no nitrogen anywhere – so no RothC reference can be a source for
these numbers. Naming one made an undocumented coefficient set read as
a sourced one (whep#346).
The values move published nitrogen: every soil-carbon stock change is divided by one of them to reach mineralized or sequestered nitrogen. Whether to cite Cleveland & Liptzin for the mineralization ratios, and what to cite for the rest, is whep#346 and still open.
What the asymmetry represents
The two directional ratios are not two process stoichiometries. They express the FLEXIBILITY of soil C:N: a soil gaining carbon is expected to move to a wider ratio, a soil losing carbon to a narrower one, so the pair brackets the bulk value. Cropland is 8 – 10 – 11 and non-cropland 11 – 15 – 15.
This is why both are documented as applying to the net change: the ratio describes where a given soil's C:N is heading, which is a property of the soil, not of an individual crop or field on part of it. Applying the choice at a finer grain than the soil makes the two directions non-cancelling and manufactures nitrogen at a soil whose carbon did not change.
The bounds themselves remain unsourced; see the source section below. What is wanted is a published marginal C:N – the ratio of the CHANGE in soil carbon to the change in soil nitrogen – not a bulk soil C:N, which is a different quantity.