Measuring and Monitoring Soil Carbon - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 195

First vertex is
random point
from centre point

Subplot A

6 m

18 m

Soil sample
location

Point
location

Samples shifted 30 cm
on successive sample
periods

Subplot C Subplot B

Ball marker

Fig. 16.1. Possible layout for a soil-monitoring site. (From Spencer et al ., 2011, with kind permission of
Taylor & Francis.)

organo-mineral soil. A common practice is
to sample mineral layers both by depth in-
crement in the site as well as by pedogenetic
horizons in a soil pit, located in close prox-
imity to the monitoring site (Arrouays et al .,
2012) or in the centre of the monitoring plot
( Fig. 16.2 ). Sampling to depths greater than
20- 30 cm is recommended ( Table 16.2 , also:
Batlle-Bayer et al ., 2010; Schrumpf et al .,
2011), as adoption of too shallow a sampling
depth may preclude the conversion to SOC
stock on an equivalent mass per area basis
(Ellert and Bettany, 1995), which is the recom-
mended practice (Wendt and Hauser, 2013).
Consideration of a fixed depth for reporting
possible SOC changes will further ignore
the effect of land-use change induced modi-
fications in bulk density (e.g. compaction).
Estimation of SOC stocks based on a definite

differences in sites and soil cores as com-
pared to the fixed depth method, due to the
negative relationship between SOC concen-
tration and bulk density (Schrumpf et al ., 2011).
For pragmatic reasons, the IPCC method for
national inventories considers SOC stock
changes expressed on a volume basis to
30 cm depth (IPCC, 2006; Ravindranath and
Ostwald, 2008), which is a simplification
(Batjes, 2011a; Wendt and Hauser, 2013).

Analytical procedures

Most organizations implementing SMNs use
long-established laboratory methods, and these
can vary greatly between and within coun-
tries (Pleijsier, 1989; De Vos and Cools, 2011).
This diversity can pose problems when using