Agriculture Reference
In-Depth Information
Table 27.1.
Changes in topsoil (0-20 cm) SOC content of China's croplands over 1985-2006, as revealed
by data from different data sets.
Data set
Land use
a
Initial (g kg
-1
)
Final (g kg
-1
)
Reference
National soil fertility
network
Rice paddy (112)
18.43 ± 7.72
19.82 ± 7.47
Cheng
et al
., 2009
Dry croplands (187)
10.46 ± 5.89
11.05 ± 6.00
Soil quality change
studies
Rice paddy (404)
15.74 ± 6.06
17.37 ± 6.31
Pan
et al
., 2009c
Dry croplands (677)
10.06 ± 6.72
10.83 ± 5.86
Long-term fertilization
experiments
Rice paddy (135)
16.28 ± 6.00
18.83 ± 7.94
Wang
et al
., 2010
Dry croplands (346)
8.99 ± 6.02
10.61 ± 6.13
Long-term tillage
experiments
Rice paddy (37)
13.02 ± 5.18
14.15 ± 5.44
Wang
et al
., 2009
Dry croplands (51)
9.29 ± 5.53
10.01 ± 5.36
a
The number in brackets is the observation number.
plant health, as well as for ecosystem func-
tioning. Several studies conducted on field
soils have indicated that SOC sequestration
may have a number of co-benefits for crop
production and agroecosystem functioning.
These benefits may include the following.
soil region of Jiangxi (Pan and Zhao, 2005).
Data from the experiments of the long-term
monitoring system for soil fertility and fer-
tilizer efficiency, managed by the Chinese
Academy of Agricultural Sciences, showed
a wider variability of rice and wheat in sites
with low background SOM levels than with
high levels (
Table 27.2).
This finding high-
lights the role SOM enhancement can play in
sustaining crop production in the face of en-
vironmental disturbance such as climate
variability. We argue that higher SOC seques-
tration with SOM accumulation could have
not only a synergic effect on increasing rice
yield but also on sustaining productivity
against environmental stresses (Lal, 2004a;
Pan
et al
., 2009b). In particular, recent field
experiments with biochar soil amendments
to enhance the stable organic matter pool
support the hypothesis that biochar has a
stimulating effect on SOM by encouraging
root system development of dry crops, in-
cluding maize, growing in SOM-depleted
soils in arid regions (Zhang
et al
., 2010, 2012).
Enhanced crop productivity
and stability
As mentioned in previously, the role of SOM
in sustaining crop production is well recog-
nized. This has been addressed in many
long-term experiments. In a study of a long-
term fertilization, Pan
et al
. (2009b) demon-
strated an increasing yield with SOM accu-
mulation under combined organic/inorganic
fertilization in east China, which was at-
tributed to the increased nitrogen (N) use
efficiency with SOM accumulation. This is
further supported by observations of yield
changes with SOM accumulation in rice
paddies under long-term fertilization studies
in south China (Yuan
et al
., 2004; Pan and
Zhao, 2005). In one of our long-term experi-
ments with conservation tillage, a signifi-
cant correlation between relative changes
in crop yields and relative changes in SOC
were observed
(Fig. 27.1)
. However, some of
our long-term field studies have shown fur-
ther benefits for the enhancement and sus-
tainability of crop productivity. Much lower
yield variability over years was observed in
plots with high SOC contents under com-
bined organic/inorganic fertilization from
long-term fertilization experiments from the
Tai Lake region of Jiangsu and from the red
Retention of N and P, and reduction
of N
2
O emission in croplands
There have been many studies demonstrat-
ing a controlling role of SOM in the reten-
tion of N in soils. This leads to a reduction
of N release to waters and enhances N use
efficiency in agricultural soils. It is already
well known that soil N contents are well
correlated with SOM levels in natural and
agricultural soils. Increase in SOM content
generally leads to an increase in the soil's
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