Agriculture Reference
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effects on improving the SOC pool at different experimental sites. The use of organic
manures has been widely practiced across China for millennia (Bi et al. 2009). This
traditional method of improving soil fertility without chemical fertilizer application
has supported the large population in China and maintained soil quality (especially
the SOC pool). The present data show that the beneficial impact of using organic
manure can be enhanced when used in combination with chemical fertilizers.
7.3.2.3 UF
The impact of using N, P, and K fertilizers separately changed the mean SOC pool
by 0.8 Mg ha −1 . The maximum and minimum changes in SOC pool were 4.2 and
−3.6 Mg ha −1 , respectively. While the SOC pool increased in comparison with CK,
the magnitude of change was lower than that for O, CF, UFO, and CFO. The impact
of chemical fertilizer separately on the SOC pool in the HHH is a debatable issue.
Zhang et al. (2002) reported that the use of chemical fertilizer merely maintained the
SOC pool. In contrast, the results of the present study show that the impact of using
chemical fertilizer separately on the SOC pool was not as strong as that of using
combined chemical fertilizer N, P, and K in combination with organics.
7.3.2.4 CF
The average increase in SOC pool through the use of combination of chemical fertil-
izer was 1.8 Mg ha −1 . The maximum and minimum changes in SOC pool were 13.1
and −3.4 Mg ha −1 , respectively. In comparison with CK as the baseline, the differ-
ence in ΔSOC pool between CF and UF was about 1 Mg ha −1 . Thus, use of combined
fertilizer is preferred.
7. 3 . 2 . 5 C F O
The average increase in SOC pool was 5.4 Mg ha −1 . The maximum and minimum
changes were 37.3 and −1.02 Mg ha −1 , respectively. The CFO treatment registered the
maximum increase in SOC pool compared with other treatments. Use of inorganic
fertilizers in combination with organic amendments is the best strategy to increase
the SOC pool for the principal crop rotation of winter wheat and summer maize in
the HHH. The straw/grain ratio is 0.8 and 1.0 for summer maize and winter wheat,
respectively (Lei et al. 2005). The HHH has a high agronomic production. Thus,
recycling of crop residues and a judicious use of fertilizers are the effective tech-
niques to increase the SOC pool. Indeed, application of fertilizer has increased the
SOC pool in the HHH (Piao et al. 2009).
7. 3 . 2 . 6 U F O
The average increase in SOC pool in the UFO treatment was 4.8 Mg ha −1 . The maxi-
mum and minimum changes were 33.4 and −3.1 Mg ha −1 , respectively. The magni-
tude of increase in SOC pool in UFO was more than those for UF, CF, and O. These
results are in accordance with the survey of SOC change (1980-2006) conducted in
Daxing County (Kong et al. 2009).
The technical potential of SOC sequestration in the UFO, CF, O, UF, and CK fer-
tilizer managements was 0.91, 3.46, 3.92, 4.6, and 5.4 Mg ha −1 , respectively. On the
basis of fertilizer use in arable land (Deng et al. 2010), the total technical potential
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