Agriculture Reference
In-Depth Information
dose and the other part was top dressed for wheat; and all chemical fertilizers were
top dressed for maize (Guo et al. 1998; Zhang et al. 2002; Zhang et al. 2005; Xia et
al. 2008; Lin et al. 2009).
7.2.3 d
AtA
A
nAlySeS
And
C
AlCulAtiOnS
For the purpose of macro-level studies, all treatments are grouped into six fertilizer
managements based on >76 different treatments at eight experimental sites across
the HHH (Table 7.2): (i) no chemical fertilizer or organic manure application as the
control treatment (CK); (ii) chemical nitrogen (N), phosphorus (P), and potassium (K)
fertilizers applied separately and without organic manure (UF); (iii) combined appli-
cation of chemical fertilizer N, P, and K without organic manure (CF); (iv) wheat and
maize straw retention or use of manures including that from soybean (
Glycine max
)
cake, chicken, horse, and cow dung or manures only (O); (v) combined application
of chemical fertilizer N, P, and K and organic fertilizers (CFO); and (vi) combined
application of chemical fertilizer N, P, or K separately and organic fertilizers (UFO).
The different fertilizers used were grouped into chemical fertilizers and organic
manure; however, the amounts of chemical fertilizer and organic manure applied
were not the same for the six categories described above. The application rates ranged
from 90 to 360 kg ha
−1
for N, from 60 to 150 kg ha
−1
for P, and from 82.5 to 250 kg
ha
−1
for K. The amount of organic fertilizers used also varied among the eight experi-
mental sites. Organic manure fertilizers were converted into C, N, P, and K, according
to the ratio of C/N and C/P for different organic manures (Lei et al. 2005). Nutrient
application rate ranged from 12 to 120 kg ha
−1
of N, from 12-170 kg ha
−1
of P, and
from 30 to 200 kg ha
−1
of K as organic fertilizers among all the experimental sites.
The data on SOC concentration (Table 7.3) were normalized and converted to SOC
pool (Li et al. 2007) by using Equation 7.1:
SOC pool (Mg ha
−1
) = SOC (g kg
−1
) × 10
4
m
2
ha
−1
× 0.2 m × SBD (Mg m
−3
) × 10
−3
(7.1)
TABLE 7.3
Descriptive Statistics of SOC in Different Fertilizer Management Treatments
SOC (Mg ha
−1
)
Fertilizer Treatments
N
Mean
Standard Deviation
Minimum
Maximum
CF
204
7.2
b
0.6
5.5
8.6
O
107
7.2
b
0.8
5.5
10.0
UF
172
6.9
ab
0.5
5.7
8.1
CFO
282
8.5
c
2.4
6.0
20.6
UFO
238
8.3
c
2.6
5.5
19.4
CK
110
6.6
a
0.6
5.2
8.0
Total
1113
7.7
1.9
5.2
20.6
Note:
Means followed by different letters differ from each other at the 5% level of probability.
