Measuring and Monitoring Soil Carbon - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 196

46

OC content
(g C kg -1 )

42

38

34

30

26

22

Fig. 16.2. Example of 'proximal sensing' approach for a field in Luxembourg. (From Stevens et al ., 2010.)

Morvan et al ., 2008). Adoption of a common
standard (e.g. ISO TC 190 Soil Quality), how-
ever, would preclude comparison with earl-
ier historic records, unless a set of reference
samples could be analysed using both the
new and 'old' methods. For example, dry
combustion for SOC may be advocated rather
than the more commonly used and cheaper
Walkley and Black method, requiring the de-
velopment of correction factors for incom-
plete oxidation (Lettens et al ., 2007; Matus
et al ., 2009; Meersmans et al ., 2009).
Harmonization may be defined as the
minimization of systematic differences be-
tween different sources of environmental
measures (Keune et al ., 1991). There are some
opportunities for harmonizing historic data
obtained using different analytical methods,
for example using regression analysis, but
these are limited (Vogel, 1994; Cools et al ., 2006;
Panagos et al ., 2013). Generally, a comprehen-
sive comparison will require the establishment
of benchmark sites devoted to harmonization

and intercalibration of conventional soil
analytical methods (Wagner et al ., 2001;
Kibblewhite et al ., 2008; Morvan et al ., 2008;
Gardi et al ., 2009). For each of these sites,
key soil properties should be measured ac-
cording to several (commonly used) analyt-
ical procedures, as well as the new standard
reference method (e.g. ISO TC 190). In prin-
ciple, this would allow comparison with re-
sults from earlier campaigns through the
use of pedotransfer functions, which, inher-
ently, will add uncertainty to the predicted
values. There are no studies yet to assess
how many calibration sites would be neces-
sary for the world and how these sites may
best be geo-located (Arrouays et al ., 2012);
interlaboratory comparisons remain critical
here (van Reeuwijk, 1998; Cools et al ., 2006).

Novel measurement techniques

Cost-effective techniques are needed to pro-
cess the bulk of data derived from large