Organic Carbon Sequestration Potential and the Co-Benefits in China’s Cropland - Principles of Sustainable Soil Management in Agroecosystems - page 512

return and the present SOC level (Pan et al. 2010) would be the sequestration potential
under BMP. By such an approach, Cheng et al. (revision submitted) estimated a poten-
tial of 0.91 and 1.01 Pg SOC, respectively, for rice paddies and dry croplands of China.
The estimated overall potential of 2 Pg is also similar to that by Lal (2002). However,
it is also argued that a technically attainable SOC sequestration potential may be much
smaller than these estimates mainly via biophysical saturation methods (Cheng et al.,
revision submitted). Constraints of technology adoption and potential area for BMPs
will still exist; for example, conservation tillage with crop residue return will not be
adopted in all of China's croplands. Therefore, an assessment of technically attain-
able SOC sequestration potential would be more appropriate to identifying the useful
approaches for mitigation of climate change by improving China's agriculture.
18.4 CO-BENEFITS OF SOC SEQUESTRATION FOR CROP
PRODUCTION AND ECOSYSTEM HEALTH IN CROPLANDS
Several studies conducted on field soils have indicated that SOC sequestration may
have a number of co-benefits for crop production and agroecosystem functioning.
Those conducted at the site level or plot level have already demonstrated a strong
benefit of SOC sequestration for crop productivity and sustainability. The high SOC
sequestration rate found in two sites of long-term agroecosystem experiments from
South China (Zhou et al. 2006, 2009; Pan et al. 2003) could be partly attributed to
enhanced chemical stabilization through binding with iron oxyhydrates (Zhou et
al. 2009; Song et al. 2011). In both of these sites, much lower yield variability over
the years was observed in plots with high SOC contents under combined organic/
inorganic fertilization (Pan and Zhao 2005). The high productivity is more evidence
of a major benefit of SOC sequestration for crop production, suggesting that SOC
sequestration can substantially enhance food production sustainability of agriculture
in croplands that are low in SOC stock. Data from long-term experiments on rice
paddies from South China ( Figure 18.7 ) and from cropland productivity monitor-
ing sites ( Figure 18.8 ) revealed that higher SOC sequestration coincided with high
rice yield and is also indicated by a high N use efficiency under combined organic/
inorganic fertilization (Pan et al. 2009). While there were few studies on SOM
effect on crop growth, field experiments with biochar soil amendment to enhance
the SOM pool support a stimulating effect of biochar added SOM on root system
development of dry crops, including maize, in soils already depleted of SOM in arid
regions ( Figure 18.9 ). This would be an indispensible reason for SOM's role in crop
production.
There has been increasing evidence that SOC sequestration could lead to a healthy
soil microbial community. With SOC sequestration, enhanced microbial abundance
and gene diversity are observed under combined organic/inorganic fertilization in
rice paddies (Zhang et al. 2004a). Jin et al. (2012) demonstrated that soil micro-
bial community and diversity and soil enzyme activity were greatly enhanced with
an increase in SOC storage in rice paddies converted from sandy wetlands in the
Hubei Province. This could be the intrinsic mechanism whereby SOC accumulation
enhances soil productivity through a buildup of an active and healthy soil microbial
community in rice paddies.