Agriculture Reference
In-Depth Information
loss, attributed to historic land misuse and soil mismanagement, can be restored by
conversion to a restorative fertilizer and adoption of recommended management
practices (RMPs) (Dao 1998; Allmaras et al. 2000; Dao et al. 2002; Lal 2004).
Increase in SOC pool by the adoption of RMPs has also been documented in China's
croplands at national (Pan et al. 2010; Wang et al. 2010), provincial (Cao et al. 2003),
and county scales (Kong et al. 2009), as is evidenced by data from long-term agro-
experimental sites (Huang et al. 2006). Adoption of RMPs is important in enhancing
the SOC pool, increasing crop productivity, and mitigating climate change. Thus,
estimating the SOC sequestration potential under different fertilizer managements is
a researchable priority, especially in the HHH agroecosystems of China.
The HHH is the primary wheat (
T. aestivum
)-maize (
Z. mays
) growing area in
China. The region comprises ~16% of China's cropland (Lei et al. 2005). The HHH
produces 60%-80% of China's wheat and 35%-40% of its maize (Kong et al. 2014),
and is the most intensively cultivated region in the country. The average yield (kg ha
−1
)
increase between 1985 and 2009 was from 1582 to 5860 for wheat and 4492 to 5610 for
maize. The present yields are 1.25 and 1.07 times the national average yield of wheat
and maize in China. The dramatic increase in crop yields and production in the HHH is
driven by intensive irrigation and the high rates of N, P, and K use since 1960, and aver-
aging 1.66, 4.43, and 1.46 times the national average rates for China (Kong et al. 2014).
The increase in SOC since the 1980s was reported by Piao et al. (2009) and Huang
and Sun (2006) in parts of China. However, the changing trends of SOC and the
mechanism of increase across the entire HHH region are not completely understood.
Thus, data from eight long-term experiments for monitoring SOC change under dif-
ferent soil fertility management treatments over time were collected and collated to
determine the temporal trends in SOC pool. Therefore, the objective of this chapter is
to evaluate the long-term effects of different fertilizer and management practices on
the SOC pool of representative soils and biomes across the entire HHH region. These
sites are representative of the smallholder farms widely distributed in the region.
7.2
MATERIALS AND METHODS
7.2.1 S
tudy
A
reA
And
SOC A
nAlySiS
The HHH plains, located in northern China, are formed by alluvial sediments depos-
ited by three rivers (i.e., the Huang River or Yellow River, Huai River, and Hai River)
(Figure 7.1). These are the largest plains and constitute an important agricultural
region in China, covering 320,000 km
2
, with 18.67 million hectares (Mha) of farm-
land and a population of 200 million (Liu et al. 2010). The region is characterized by
the intensive use of irrigation and chemical fertilizers, and the predominant cropping
system in the region is double cropping of winter wheat and summer maize.
The SOC concentration was measured from eight long-term experimental sites
in which the plots were managed by the Ministry of Agriculture, People's Republic
of China (Figure 7.1). The climate and soil properties of the study sites are shown in
Table 7.1. The annual rainfall ranges from 461.9 to 837.3 mm, the annual cumulative
temperature from 4874.0 to 5368.2 degree days, and the annual average temperature
from 12.8°C to 14.6°C.
