Agriculture Reference
In-Depth Information
BACKGROUND OF NATURAL ENVIRONMENT OF CHINA
Environmental Factors
China has an area of about 9,600,000 square kilometers, extending from about 22 to 55
N and
ο
78 to 135
E. Within the vast territory, there are various soil types developed under different
bioclimatic conditions and derived from various parent materials in diversiÝed topographical envi-
ronments. The relief of China can be divided into three steps or levels. The highest level is the
Qinghai-Xizang Plateau with an altitude of more than 4000 m. The second level is from the plateau
going northward and eastward to the line of the Da Hinggan Ling, the Taihang Mountains, the
Wushan Mountains, east slope of the Yunnan-Guizhou Plateau, and most of the basins in the regions
are between 1000 to 2000 m above sea level. The third level is composed of rolling hills and coastal
plains where the hills rarely exceed 500 meters in height (Figure 10.1). This highly contrasting
topography inÞuences orographic changes and the penetration of the humid tropical PaciÝc air
mass into the western inland. The range of climatic conditions superimposed on the geologic and
topographic situations results in a wide variety of soils and soil conditions.
In the Tertiary and Quaternary Periods, geologic activities affected the soil formation predom-
inantly, and consequently the formation of the main soil types is strongly inÞuenced by their parent
rocks. Thus in the mountainous regions of northeastern China, Inner Mongolia, and eastern and
southern China, the soil-forming materials are mainly granite, rhyolite, andesite, and basalt. In the
coastal and delta areas, they are mainly alluvial deposits, and in the northwestern plateau and the
North China Plain, they are loessial deposits. Red earths of southern China are mainly derived
from Quaternary red clay and Tertiary red sandstone, while the glacial deposits often appear on
the Qinghai-Xizang Plateau.
Redox processes govern the geochemistry of soil formation and, as a result, the weathering
products are divided into oxidizing and reducing crusts. The oxidizing crust is further divided into
Ýve types, i.e., fragmental crust resulting from mechanical disintegration of rocks; gypsum and salt
crust in the inland basins and salt lakes of the desert areas in Xinjiang Basins and Qinghai-Xizang
Plateau; carbonate crust in the Northwest Plateau, the North China Plain, and the central and
southern parts of the Qinghai-Xizang Plateau; siallitic crust containing laminated clays of 2:1 type
as dominant clay minerals associated with vermiculite and transitional clay minerals; and allitic
crust in South China (Gong et al., 1997).
China has a very distinctive monsoon climate. In summer, high temperature prevails in both
North and South China, but in winter, the climate is very cold in the north and rather warm and
mild in the south. According to the temperature variations, Ýve climate zones can be classiÝed,
i.e., the cool temperate zone, temperate zone, warm temperate zone, subtropical zone, and tropical
zone. The regions are differentiated using an index called Ñaccumulated temperatureÒ which is the
product of the number of days when the temperature is >10
ο
C and the temperature of each of these
days. Northern Heilongjiang Province, where the frostless season is about three months with an
accumulated temperature of
ο
≥
10
C being less than 1,700
C belongs to the cool temperate zone.
ο
ο
The first level
Hengduan Mt. The second level
Sichuan Basin
(m)
Qinghai
Xizan
g Plate
au
100
°
90
°
Figure 10.1
Sketch of topographic section of China. (From Xiong et al., 1987. With permission.)
