Benefits of SOM in Agroecosystems: The Case of China - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 315

historical development of world agriculture,
scientists have put increasing emphasis on
the degradation of agroecosystems due to the
depletion of SOM under intensified crop-
ping and increasing chemical fertilization
(Feller et al ., 2012).
Based on statistics of cropland topsoil
organic matter contents and the crop yield
changes across a time span from 1949 to
1999, Pan et al . (2009a) were able to draw a
linear relationship between mean cereal
productivity and average cropland SOM
contents in provinces of China. However,
the incremental response depends on cli-
matic conditions and socio-economical and
technological factors. The dependency of
crop yield on SOM appears to have de-
creased in recent times, probably due to the
enhanced technology input with econom-
ical development. This is also seen in an
analysis of crop productivity in relation to
SOM and the variation between the regions
of China, where mean provincial cereal
yield in the major crop producing provinces
is strongly related to mean topsoil SOM
contents in north China as well as in Jiangsu
and Shanghai during 1949-1999 (Pan et al .,
2013). Taking the example of Jiangsu, one of
most developed provinces in China, a good
correlation between both agricultural out-
put and gross domestic product (GDP) could
be found with cropland SOM levels for the
time before 1985 and in 2004 (Pan et al .,
2013). These findings clearly show that the
SOM level is not only very important for
agricultural production but also for regional
economic development, presumably due to
enhanced production and ecosystem func-
tioning with SOM accumulation in soils.

been a cause for concern from the perspective
of both land degradation and greenhouse gas
(GHG) emissions (Feller et al ., 2012). As esti-
mated by Lal (1999), up to 5% of the original
SOM has been lost from croplands worldwide
due to land use changing from natural soils to
croplands. This has given rise to an accumu-
lative global CO 2 emission of 55 Pg C (IPCC,
1995). In a literature review of agricultural
soil research in China before 1960, Lindert
et al . (1996) voiced serious concerns over the
historical loss of SOM from a wide range of
China's ecosystems due to agricultural land use
since the 1950s. Utilizing the Denitrification-
Decomposition (DNDC) model, Li (2000)
found there had been a significant decline of
organic carbon (C) storage in China's croplands
of up to 70 Tg since the 1970s. Lal (2004b),
however, estimated a total loss of 3.5 Pg since
agricultural development in China, including
approximately 2 Pg from land desertification
caused by irrational land use and management,
as previously estimated (Lal, 2002),whereas a
statistical analysis by Wu et al . (2003) of soil
organic carbon storage from the archived se-
cond national soil survey data of cultivated
soils showed a loss of whole soil organic car-
bon stock from China's croplands of 7-8 Pg C
compared with natural soils. In their work, a
dramatic decline in organic carbon stock oc-
curred mainly in the north and other arid
and semi-arid regions of China. Nevertheless,
it has been argued that there have been large
areas and soil-land-use associations where
changes in SOM contents were either min-
imal or even positive, especially in irrigated
areas (Pan et al ., 2003). Using a similar
method to Wu et al . (2003), but using topsoil
data from the national soil survey conducted
during 1982-1985, Song et al . (2005) com-
pared soil organic carbon (SOC) levels of
cultivated soils to uncultivated soils in a
comparative analysis, and revealed that cul-
tivation induced a loss of topsoil SOC stock
of up to 14.8 ± 15.1 Mg ha - 1 . This gave a total
SOM decline of 2 Pg C due to the cultivation
of natural soils for the whole of mainland
China. In their work, over 60% of this loss
was observed to occur in soils of north-east
China, north-west China and south-west
China. Therefore, significant loss of SOM oc-
curred under intensive cultivation and in

Dynamics of SOM in China's
Croplands over the Past
Two Decades

Depletion of SOM in croplands
in the history of agricultural
development in China

In the history of agricultural development, the
depletion of SOM from cultivated lands has