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land use objectives. Similar results were reported by Rasmussen et al. (1998) and
Nyakatawa et al. (2001).
8.3.2 C hAnge in SoC C onCentrAtion from 1999 to 2006
Unlike the variable and increasing SOC concentration levels observed in 1980 and
1999, there was apparently no drastic change in the SOC concentration in soil sam-
pled in 1999 and 2006. The average SOC concentration was 6.93 g kg -1 in 1999 and
6.79 g kg -1 in 2006. Therefore, SOC concentration slightly decreased by 0.14 g kg -1
over this period ( Table 8.2 ). The CV of SOC concentration increased from 39 to 45
during the second period. The SOC concentration was similar to those observed
between 1999 and 2006. The results presented here are similar to those reported by
Niu et al. (2005).
The results suggest that change in application rate of fertilizers and the cropping
system led to a slight decrease in the SOC concentration within the county between
1999 and 2006. However, the total grain yield in 2006 for the wheat-maize cropping
system increased by 225 kg ha -1 as compared to 1999 ( Table 8.4 ).
The cropping systems changed drastically between 1999 and 2006. The major
crops were wheat and maize in 1999 but cotton in 2006 (Table 8.5). However, the
percentage of area under wheat and maize decreased by 73.1%, and that of cotton
increased by 80.6% between 1999 and 2006. This change may account for the grad-
ual decrease in SOC concentration on the whole.
8.3.3 C hAnge in SoC C onCentrAtion AS A r eSult
of C hAngeS in the C ropping S yStem
The change in pattern of SOC concentration in the same cropping system from 1999
to 2006 ( Tables 8.6 and 8.7) was as follows: (1) SOC concentration in the cropping
system of wheat-maize increased by 0.88 g kg -1 ; (2) SOC concentration increased by
7% in the cropping systems of wheat and maize; (3) SOC concentration decreased by
0.21 g kg -1 when the cropping system of wheat-maize was converted to cotton. The
TABLE 8.5
Changes in the Cropping System from 1999 to 2006
Change (%)
Cropping System
1999
2006
Variability (%)
Wheat-maize
88.06
14.93
-83
Cotton
2.99
83.58
2700
Vegetable
7.46
1.49
80
Native grassland
1.49
0
100
Source: Data from 2006 household survey.
 
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