Sustainable Soil Management Is More than What and How Crops Are Grown - Principles of Sustainable Soil Management in Agroecosystems - page 350

of southern Australia, occupy large regions of Victoria and South Australia. Soil
erosion began on these soils soon after clearing in the late 1800s. Similar erosion
occurred in Western Australia when its sandy soils were released in the early 1960s.
Prior to the availability of herbicides in the 1980s, tillage was essential for control-
ling weeds. However, the burial of surface organic matter, through tillage, exposed
the soil to the erosive forces of the wind. During wetter years, in the 1960s, the level
of erosion was small due to the rapid soil cover from regreening of annual pastures
or weeds near the “break of the season.” In contrast, the poor ground cover during
successive drought years caused serious wind erosion, which could persist for much
of the year. The mallee area of Victoria had regularly horrifying dust storms in the
1930s. In Western Australia, similar erosion occurred in the 1969 drought and regu-
larly thereafter during the dry 1970s.
During this time, pasture was often overgrazed and the soil was left bare, and this
also predisposed soil to wind erosion. The common practice, at the time, was two
preseeding tillages to control weeds and soften the soil, for even seed placement.
Similarly to sheep grazing, this tillage removed surface vegetation that could protect
the soil against erosion (Robertson 1987).
During autumn (March-May), and before the pasture or crop could fully cover the
ground with new growth, strong prefrontal winds would blow the topsoil against the
seedlings, often cutting the plants off and blowing the soil off-site. Both emerging
crops and pastures were damaged. On other sandy soils, on more hilly terrain, and in
higher rainfall areas, water erosion was more of a concern to farmers. Similarly, the
sandy soil was loosened with tillage and was also left bare, providing little soil cover
to protect the soil from water erosion.
14.3.3.3 China
In Asia, population pressure on natural resources is already high, and it is expected
to increase further. However, based on past trends, as population continues to grow
toward a plateau level of 9 to 10 billion people, the expansion of land will become
increasingly modest. The growth in commodity production in South Asia is now
almost completely (94%) based on increases in yields and cropping intensities (FAO
Agriculture Towards 2050), and available water resources are the limiting factors
there. In East and Southeast Asia, there is still a lot of water that could be used for irri-
gation, but the agricultural land resources are becoming scarce (Pisante et al. 2010).
China is one of the Asian countries that have been seriously endangered and affected
by soil degradation. The area of land degradation is estimated to be 370,000 km 2 cor-
responding to a direct economic loss of 54 billion yuan ($8.5 billion) each year. Soils
in dryland areas have suffered severe degradation and desertification through water
and wind erosion impacting the main grain-producing area of the country.
The threat of water erosion in dryland areas is affected by the amount and inten-
sity of rainfall, the type of irrigation, the erodibility of the soil, cropping and man-
agement factors, and erosion control practices. The impact of raindrops or the flood
irrigation on the soil surface is the beginning, and the most important part, of the
erosion process. In recent decades, sand storms in China have also done great harm
to the farmland. As affected by all the reasons mentioned above, the degradation of
farmland finally caused the decline of productivity.