Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 351

Annual rainfall ranges from 200 to 600 mm in the Loess Plateau, which is a one
crop per year region. Soil in the Loess Plateau is easily eroded and is intensively
cropped with dryland winter wheat. Limited crop-available water is one of the major
factors constraining agricultural production on the Loess Plateau, and severe erosion
has resulted in degradation of soil properties, such as water retention (Zha and Tang
2003).
In cold and semiarid Northeast China, spring maize is one of the most important
grain crops in terms of area and output (Liu et al. 2002). The annual rainfall here
varies from 400 to 1000 mm, and the average cumulative evaporation is ~1800 mm,
which is about four times higher than the average total rainfall received during the
growing stage of spring maize. Therefore, the low status of soil moisture in the root
zone usually limits productivity of spring maize in this region. Conserving moisture
accumulated in the root zone during the rainfall season can increase productivity of
spring maize in the dry Northeast China.
In annual double cropping areas of the North China Plain, the annual rainfall is
450 to 800 mm, and the annual cumulative evaporation hugely exceeds the annual
rainfall. Since the 1980s, the cropping system in this region has changed from a
single- to a double-cropping system (winter wheat-summer maize) (Liu 2004).
Therefore, the demand for plant available water has jumped and water scarcity is a
serious issue.
In the pastoral ecology of Inner Mongolia, the annual rainfall is 450 to 500 mm,
and the annual cumulative evaporation is 1300 to 1880 mm, hugely exceeding the
annual rainfall. In some parts of the pastoral areas, the annual rainfall is even less
than 50 mm (He et al. 2009a). In the last 100 years, large areas of grassland have
been converted into cropland due to an increased population and food demand
(Zhang et al. 1998). The agriculture-pasture transition region has about 32.8 Mha
land, representing 27.8% of the total land area of Inner Mongolia (LZU 2005). In this
region, conversion of grassland to cropping combined with insufficient rainfall and
wind erosion has resulted in serious soil nutrient depletion and structural deteriora-
tion (Liu et al. 2007).
In Northwest China, water shortage is one of the major constraints to the produc-
tion of agricultural crop. The average annual precipitation varies from 40 to 200 mm
(Xie et al. 2005), and the annual potential evaporation in this region exceeds
1500 mm resulting in a moisture deficit of at least twice the growing season require-
ments of spring wheat for the area (>600 mm).
The dryland areas of China have soil that are easily eroded and intensively cropped
with dryland crops (wheat, maize, etc.), which occupy 56% of the arable land (Zhu
1989). Over the past 20 years, crop yields have increased through fertilizer applica-
tion and increasing water consumption; however, soil water is often not fully replen-
ished during the fallow period (Huang and Zhong 2003). Since crop yield varies
strongly with rainfall (Li 2001), water shortage becomes the greatest threat to crop
production. Some 80% to 90% precipitation is lost through evaporation or runoff,
and only 10% to 20% can infiltrate into the soils. Thus, the soil water storage capac-
ity is a crucial indicator for increasing production (Li et al. 2007; Zhang et al. 2009).
Conventional tillage practices based on moldboard plowing and preparing fine
seedbeds with residue removed or burned have resulted in poor soil fertility and