Benefits of SOM in Agroecosystems: The Case of China - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 322

SOC-poor plots under long-term agroeco-
system experiments (Williams et al ., 2007).
Decreases in soil respiratory activity with
increase in SOC have been observed in dry
croplands under organic fertilization in
comparison with those under non-organic
amendments (Meng et al ., 2005; Yin and Cai,
2006). An integrated field study using a
number of long-term experiments from rice
paddies in south China demonstrated an in-
creasing dominance of the fungal over the
bacterial community with increasing SOC
accumulation. This in turn supports a re-
duction both in soil respiratory quotient and
microbial metabolic quotient under good
agro-management (Liu et al ., 2011). A labora-
tory incubation study of methane production
from rice paddies differentiating in SOC con-
tents also characterized a reduction in C in-
tensity from methane emission in rice paddy
containing high SOC under combined or-
ganic/inorganic fertilization. This is further
proven by another study with enhanced
diversity of methanotrophs, which is respon-
sible for methane exhaustion in rice paddies
(Zheng et al ., 2008). A soil fauna study by
Xiang et al . (2006) documented an en-
hanced size of the soil fauna community
and enhanced diversity, especially those of
soil earthworms, thus favouring soil aggre-
gation and nutrient accumulation (Wang
et al ., 2009) in a long-term experiment site
from the Tai Lake region, China.
A new insight into SOC sequestration
and GHG emission was that a total global
warming potential calculated from all the
GHG fluxes in a plot continuously receiving
compound fertilizers seemed smaller than
from the one receiving the chemical fertilizer
only (Li et al ., 2009a,b; Liu et al ., 2009).
Some studies have shown that the net C sink
can be 1.5- 3 times more under a combined
organic/inorganic fertilizer regime than that
under chemical fertilization in rice paddies
from Jiangxi and Jiangsu, China (Li et al .,
2009a,b). A similar study indicated that there
was a higher net C sink (by 1.1- to 1.7-fold)
under organic amendments compared to under
chemical fertilization only (Peng et al ., 2009).
In addition, as mentioned above, in-
crease in N efficiency could help to decrease

fertilizer-induced C emission per unit of rice
production, in turn resulting in a higher net
C sink (Li et al ., 2009a,b). And this has also
been true for the rice paddy in a site of
Jiangxi where a higher rate of SOC seques-
tration has been observed (Li et al ., 2010).
Thus, SOC sequestration in croplands, par-
ticularly in rice paddies, would offer mul-
tiple win-win effects for crop productivity
and mitigation of GHG emission, as well as
ecosystem health in agriculture, so ensuring
food security and sustainability of agricul-
ture for China (Pan and Zhao, 2005).

Benefits for soil chemical buffering

In a recent study of soil acidity changes over
1985-2006 in croplands of soil-monitoring
sites over China, the extent of soil pH
change was shown to be largely dependent
on SOM level ( Fig. 27.5 ). Thus, the role of
SOM accumulation in buffering chemical
processes of croplands is clearly demon-
strated. However, this has been poorly as-
sessed in soil or geosciences research.

Conclusion

In conclusion, increase in SOM content
would lead to an increase in soil's capacity
to act in an integrated and interactive manner
for cropland productivity and ecosystem
health. In the case of China, accumulation
of SOM may have a number of benefits for
agricultural production and nutrient use
and in sustaining a good quality of agroen-
vironment. We hypothesized that input of
OM to soil might progressively lead to a
build-up of soil aggregates with diverse
soil microhabitats, a healthy soil microbial
community with greater fungal dominance
and higher diversity for ecological re-
dundancy. In this way, functional entity is
developed with mutual interaction of
mineral, chemical, biological and ecological
forces. Therein, soil processes and func-
tioning could be magnified to enhance soil
capacity for nutrient, moisture and biotic