Agriculture Reference
In-Depth Information
TABLE 7.5 (Continued)
Trend Line Regression Equations of Temporal Changes in SOC Pool for
Different Fertilizer Managements
Threshold
SOC Pool
(Mg ha
−
1
)
Treatments
Region
Trend Model
Years
R
2
CK
XinjiA
y
= 0.21
x
+ 16.51
R
2
= 0.51**
20.00
20.76
XinjiB
y
= 0.09
x
+ 18.51
R
2
= 0.41*
20.00
20.35
Xuzhou
y
= −0.42
x
+ 16.83
R
2
= 0.73*
0.00
16.83
Changping
y
= −0.23
x
+ 21.21
R
2
= 0.54*
0.00
21.21
ZhengzhouA
y
= 0.03
x
+ 20.37
R
2
= 0.00
18.00
20.89
ZhengzhouB
y
= −0.05
x
+ 18.91
R
2
= 0.00
0.00
18.09
HenshuiA
y
= −0.05
x
+ 17.83
R
2
= 0.10
0.00
17.83
HenshuiB
y
= 0.01
x
+ 19.05
R
2
= 0.01
23.00
19.24
* Significance of the SOC pool trend at
P
< 0.05.
** Significance of the SOC pool trend at
P
< 0.01.
*** Significance of the SOC pool trend at
P
< 0.001.
7.4 CONCLUSIONS
The data presented support the following conclusions:
1. The SOC pool for CK was maintained at the stable baseline level between
1978 and 2003 at 18.9 ± 1.8 Mg ha
−1
.
2. The SOC pool in other fertilizer and management treatments generally
increased in comparison with that of CK for all experimental sites in the
HHH. The average change in SOC pool was 0.8,
1.9, 1.6, 4.8, and 5.4 Mg
ha
−1
for UF, CF, O, UFO, and CFO, respectively. The increase in SOC pool
was much higher in treatments involving the combined use of chemical
fertilizers and organic manures compared with chemical fertilizer alone.
3. The rate of change of SOC pool varied over time; the MR of increase ranged
from 224.4 to 1969.7 kg ha
−1
year
−1
for CFO, and the AR from 74.0 to 1529.6
kg ha
−1
year
−1
.
4. The trend line of SOC pool over time for UFO and CFO for all experi-
mental sites indicated a rapid increase throughout the experimental dura-
tion, while it maintained a steady-state (stable) level for CK, UF, CF, and
O treatment.
5. There were threshold levels of SOC pool for CFO and UFO, and the maxi-
mum values for XinjiA, XinjiB, and Xuzhou sites were 42.1, 34.2, and 26.4
Mg ha
−1
with the durations to attain these maximum of 21.0, 41.9, and 15.7
years, respectively. The maximum SOC pools under UFO for the XinjiA,
XinjiB, and Xuzhou sites were 42.8, 26.4, and 34.2 Mg ha
−1
with the corre-
sponding experimental durations of 23.0, 20.0, and 15.8 years, respectively.
