Agriculture Reference
In-Depth Information
a result of cultivation (Reeder et al. 1998). Some studies have reported that increase
in SOC concentration is correlated with the amount of crop residues that have been
returned to the topsoil (Hendrix et al. 1998; Peterson et al. 1998; Janzen et al. 2004).
Many studies have been conducted on the effect of different tillage practices on
SOC concentration in different regions of China, such as hilly regions (Guo et al.
2001; Li et al. 2006b), the Loess Plateau (Fu et al. 1994, 1999a,b, 2000; Li et al.
2006a; Pang and Huang 2006), and the Karst area (Long et al. 2002). The North
China Plain (NCP) is the region with the most intensive agriculture in China, and
the effects of change in the cropping system and its impact on the SOC concentra-
tion must be studied in relation to quality of soil and the environment. There have
also been studies on the effects of intensive farming (Qi et al. 2001) in this region
and its impact on the SOC concentration (Kong et al. 2006). However, the change in
the SOC concentration with respect to the effects of change in cropping systems in
relation to transition of family farming to profit farming are not yet well understood.
China, as the most populous and rapidly developing country, has experienced
great economic development, which has strongly shifted the family farm objectives.
This transition has led to the increased use of fertilizer and changes in the cropping
system. During the 1980s, the goal of the family farm was to meet its own food
needs. However, the farmers had no choice but to increase crop yields by convert-
ing native land to farmland. The major cropping system in the region is maize (
Zea
mays
), wheat (
Triticum aestivum
), and cotton (
Gossypium hirsutum
).
Therefore, the purpose of this study was to analyze the change in SOC concentra-
tion in different cropping systems upon transition from family farm to profit maxi-
mization with different economic development. The expansion of farms in relation to
choice of cropping systems and increased use of fertilizer according to different eco-
nomic development phases were the major variables (Kong et al. 2004a; Angelsen
1999). Change of SOC concentration in two crop rotation systems, including con-
tinuous cultivation of winter wheat-maize from 1980 to 2006, and the conversion
from winter wheat-maize (1980-1999) to cotton (1999-2006) were also assessed.
8.2
DATA AND METHODS
8.2.1 S
tudy
A
reA
The experiment was conducted in Quzhou County (36°34′-57′N, 114°13′-50′E),
northeast of Handan, Hebei Province, in the center of the NCP. This county is approxi-
mately 67,500 ha with 50,900 ha (75%) of cultivated land. The annual rainfall is
535 mm, with 67% received during the summer. The annual average temperature
is 13.2°C, and the frost-free period is 201 days. The principal soil types are light,
medium, and heavy saline fluvo-aquic inceptisols. The region has saline phreatic
water reserves (2-10 g L
-1
) (Shi 2003), which may exacerbate the risks of salinization.
The region is characterized by intensive use of irrigation and chemical fertilizers,
and the predominant cropping system is double cropping of winter wheat followed
by summer maize. This county has undergone rapid economic development in recent
years, which caused the gross domestic product (GDP) to increase by approximately
15% per year. However, the proportion of agricultural production to total production
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