Measurement and Monitoring Soil Carbon
What will the protocol deliver
Approaches in soil carbon measurement
The UNFCCC
recommended tiered approach ranging from a simple (tier 1) to higher order
(tier 3) methods of estimating carbon stocks (see box below).
Tier 1 methods are
designed to be the simplest to use, for which equations and default parameter
values (e.g., emission and stock change factors) are provided in this volume.
Country-specific activity data are needed, but for Tier 1 there are often
globally available sources of activity data estimates (e.g., deforestation
rates, agricultural production statistics, global land cover maps, fertilizer
use, livestock population data, etc.), although these data are usually
spatially coarse.
Tier 2 can use the
same methodological approach as Tier 1 but applies emission and stock change
factors that are based on country- or region-specific data, for the most
important land-use or livestock categories. Country-defined emission factors
are more appropriate for the climatic regions, land-use systems and livestock
categories in that country. Higher temporal and spatial resolution and more
disaggregated activity data are typically used in Tier 2 to correspond with
country-defined coefficients for specific regions and specialized land-use or
livestock categories.
At Tier 3 higher order methods
are used including models and inventory measurement systems tailored to address
national circumstances, repeated over time, and driven by high-resolution
activity data and disaggregated at sub-national level. These higher order
methods provide estimates of greater certainty than lower tiers. Such systems
may include comprehensive field sampling repeated at regular time intervals
and/or GIS-based systems of age, class/production data, soils data, and
land-use and management activity data, integrating several types of monitoring.
Pieces of land where a land-use change occurs can usually be tracked over time,
at least statistically. In most cases these systems have a climate dependency,
and thus provide source estimates with inter-annual variability. Detailed
disaggregation of livestock population according to animal type, age, body
weight etc., can be used. Models should undergo quality checks, audits, and
validations and be thoroughly documented.
Source: 2006 IPCC Guidelines for
National Greenhouse Gas Inventories, Volume 4: AFOLU
There are two basic versions of the protocol which
are relevant for different situations.
1. Interest is in the total SOC stock of the project area
The total SOC in the project area might be of
interest if an aim of the project is to maintain or increase it.
In this case, following the protocol will give
estimates of the total SOC in the project area down to a given depth or
cumulative mass, together with an estimate of the error. The output would thus
be a single figure in tonnes, together with the error
of that figure.
Follow-up measurements after some years would
give an estimate of the new total stock with its error, and an estimate of the
change in SOC stocks during the elapsed time
2. Interest is in the variation in SOC across the project area
The variation in SOC across the project area
could be represented on a map that shows areas of lower and higher SOC.
This would be needed if the project wanted, for example, to identify where
activities to maintain high levels of SOC should be targeted or where
interventions are needed to buildup from low levels of SOC.
Following the protocol would allow a map of
current SOC stocks to be produced. It will show, for any point on the map, the
estimated SOC per square meter down to a specified depth or cumulative mass.
This is not simply a map of land use with a constant stock in each land
use area. It is a map that estimates the continuous variation in SOC both within
and between different land uses in the project area.
Follow-up measurements after some years would
give an updated map of the new distribution of SOC stocks and a map of changes
in SOC stocks.
For either (1) or (2) above you have a choice of
estimating SOC down to a given depth or cumulative soil mass. Measuring
to a fixed depth (e.g. the top 50cm) is simplest, but estimates of change of
SOC are contaminated by changes in soil bulk density. Estimating to a
cumulative mass (e.g. the top 400 kg m-2) adds data collection and
analysis complexity but corrects for changes in bulk density.
Additional requirements that the protocol could
be used to meet are:
3.
Interest is in understanding factors associated with variation in SOC
Some projects might wish to use the opportunity
of collecting SOC data to understand more about how variation within the
project area is associated with land use or soil type. The soil sampling
methods described here will be suitable but will be supplemented with
measurement of other variables. See the Land Degradation Surveillance
Framework (LDSF). In this protocol we describe the SOC measurement only.
4.
Interest is in measuring the effect on SOC stocks of specific project interventions
Some projects might wish to estimate the effect that specific
interventions have made within the project area, which are only expected to
affect some of the project area. For example, the project might want to
estimate the effect on SOC of conservation agriculture, which has only been
adopted on some plots within the area. One option is to use the methods
for measuring the whole project area only on those plots that have adopted the
intervention. However, this approach has various biases and better designs are
needed. This protocol does not elaborate on details of measuring the effect of
interventions, but simple modifications outlined can be made.
__________
IPCC.
2006 IPCC Guidelines for National
Greenhouse Gas Inventories. Volume 4: Agriculture, Forestry and Other
Land Use. Eggleston, H.S., Buendia, L., Ngara, T., and Tanabe, K. (eds). IGES, Japan.