Agriculture Reference
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FIGURE 18.9 Well-developed root system (left, dark colored, amended with biochar) in
OM-rich soil in contrast to OM-depleted soil (right, bright color) of maize in an Ochrept from
Shanxi, China. (Courtesy of Genxing Pan, May 2012.)
be lower in plots rich in SOC under a well-designed fertilizer scheme when com-
pared with relatively SOC-poor plots under long-term agroecosystem experiments,
as was reported by Williams et al. (2007). Decreases in soil respiratory activity with
increases in SOC have been observed in dry croplands under organic fertilization,
unlike those under nonorganic 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 has demonstrated an increasing dominance of the fungal over the
bacterial community with increasing SOC accumulation, which in turn supports a
reduction both in soil respiratory quotient and in microbial metabolic quotient under
good agromanagement (Liu et al. 2011). A laboratory incubation study of methane
production from rice paddies with different SOC contents also showed a reduction
in C intensity from methane emission in rice paddies containing high SOC under
combined organic/inorganic fertilization, and this is further proven by another study
with enhanced diversity of methanotrophs, which is responsible for methane exhaus-
tion in rice paddies (Zheng et al. 2008). 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 only the chemical fertilizer (Li et al. 2009a,b; Liu et al.
2009). Some studies have shown that the net C sink can be 1.5 to 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 amend-
ments compared to under chemical fertilization only (Peng et al. 2009).
Meanwhile, there have also been other studies with long-term experiments under
well-managed practices that indicated that SOC accumulation would exert additional
positive effects on ecosystem health. In coincidence with the findings of microbial
abundance and diversity, Xiang et al. (2006) documented enhanced soil fauna com-
munity and diversity, especially those of soil earthworms in a long-term experiment
site from the Tai Lake region. Conducting the same experiment used by Xiang et al.
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