Agriculture Reference
In-Depth Information
7.3.3 r
Ate
Of
C
hAnge
Of
SOC p
OOl
under
d
ifferent
f
fertilizer
m
AnAgement
t
reAtmentS
There are no definite trends in the rate of change in SOC pool, which had both maxi-
mum and minimum points. Thus, both the maximum rate (MR) and the average rate
(AR) of change in SOC pool are used to establish any trends among different treat-
ments (Figure 7.2). Both MR and AR were in the order of CFO > UFO > O > CF >
UF > CK. These results are in accordance with those reported by Pan et al. (2010)
and Wu and Cai (2007).
The range of change is 52.0 to 188.0 kg ha
−1
year
−1
for MR, and −315.5 to 84.1 kg
ha
−1
year
−1
for AR in comparison with the CK treatment. The range of increase in
SOC pool (kg ha
−1
year
−1
)
for MR and AR, respectively, is 57.4 to 299.4 and −83.1
to 214.0 for UF, 1.9 to 389.7 and −166.3 to 203.2 for CF, 76.3 to 1480.9 and 24.0 to
1345.6 for O, 176.3 to 1823.3 and 119.2 to 1594.3 for UFO, and 224.4 to 1969.7 and
74.0 to 1529.6 for CFO. The rate of change of SOC pool showed an increasing trend
over time for all the experimental sites. The analysis of MR and AR for the SOC pool
indicated a nonlinear trend exhibiting both the minima and maxima. Thus, the AR
of the change of SOC pool is not a good indicator of the instantaneous rate of change.
With CK as the baseline, the change in the SOC pool between 1978 and 2003 was
strong for UFO and CFO, with a gradual increase for O but no definite trend for CF.
These data indicate that the SOC pool in cropland cannot be increased continuously
by the application of chemical fertilizers alone. Maintenance and increase of SOC
pool in the HHH depend on the combined use of organic manures and fertilizers.
7.3.4 C
hAnge
in
SOC p
OOl
under
d
ifferent
f
fertilizer
m
AnAgementS
Over
l
Ong
-t
erm
e
xperimentS
Regression equations indicating the change in SOC pool over time under different
fertilizers and management treatments during the experimental period are shown
in Figure 7.3. The trend of change in SOC pool can be organized into three groups.
Group 1 consists of CK, which maintained its SOC pool at almost 20.0 Mg C ha
−1
between 1978 and 2003. This is the minimum stable baseline for the SOC pool in
cropland in the HHH. Group 2 consists of CF, UF, and O, which exhibited a slight
change in the SOC pool compared with that of CK: those of O and CF increased
and that of UF decreased only slightly. Group 3 consists of CFO and UFO in which
the SOC pool increased from 20.0 to 50.0 Mg ha
−1
(2.5 times or 150% increase) dur-
ing the experimental period. Therefore, regular application of organic and inorganic
fertilizers can substantially increase the SOC pool and also sustain it at a high level.
Regression equations of trend lines for different fertilizer management treatments
are shown in Table 7.5. A linear trend of change in SOC pool over time is observed
in CK, UF, CF, and O, compared with a polynomial function for CFO and UFO
( Table 7.4).
There was a threshold value of SOC pool for CFO and UFO treatments. The
maximum SOC pools for XinjiA, XinjiB, and Xuzhou were 42.1, 34.2, and 26.4
Mg ha
−1
along with the durations to attain the maximum of 21.0, 41.9, and 15.8
years, respectively. The maximum SOC pools under UFO for the XinjiA, XinjiB,
