Land degradation

Land utilization (percentage of total land area): Asia and the Pacific

Land is intensively cropped in South and Southeast Asia, with large areas of pasture in all other subregions except the South Pacific. In South Asia, more than onethird of all land is cropped Source: compiled from FAOSTAT 2001

Land degradation processes of particular concern in Asia and the Pacific include erosion, compaction, acidification, declining soil organic matter, weed infestation, soil fertility depletion and biological degradation.

The Global Assessment of Soil Degradation (GLASOD) estimated that about 13 per cent (or 850 million ha) of the land in Asia and the Pacific is degraded (Oldeman 1994) - most of this is in Asia but 104 million ha were estimated to be degraded in the Pacific sub-region where large-scale clearance of forest land has caused a decline in soil structure and fertility and where invasive species are the predominant land cover in many islands.

The most severe water erosion occurs in the Himalayas, Central Asia, China, the South Pacific and Australia, while the GLASOD study indicated that in the South Asian sub-region Afghanistan, India, Iran and Pakistan are the worst affected by wind erosion (Oldeman 1994).

Chemical soil degradation is mainly caused by agricultural mismanagement. In parts of northern India and Bangladesh, soils have been acidified and salinized, and have been losing nutrients, while a significant proportion of land in Cambodia, Malaysia, Thailand and Viet Nam has been degraded by acid sulphates (Oldeman 1994). Poor soil nutrient balances (between phosphorus, nitrogen and potassium) are common in Australia, Bangladesh, Nepal, Pakistan and Sri Lanka.

Saline soils cover 60 million ha of agricultural land in the region, and Australia in particular is facing severe land salinization problems (MoAFFA 1999). Excessive extraction from groundwater and surface water sources, and rising water tables brought about by faulty irrigation systems, have increased the occurrence of surface water and soil salinity.

Serious soil contamination problems are characteristic of the northern parts of the region, and parts of Australia and New Zealand. The contaminants include cadmium (contained in fertilizer), hexavalent chromium, lead, arsenic, trichloroethylene, tetrachloroethylene and dioxin concentrates. Health issues arising from chronic poisoning from agricultural land were common in the 1970s in the northwest Pacific and northeast Asia (MoE Japan 2000). The major soil polluters in the region are now the chemical and electroplating industries in Japan and the Republic of Korea but heavy metals are also present in agricultural land (as a result of fertilizer application), and near mines and refineries (due to chemical discharges). Soil contamination from lead and arsenic contamination is prevalent throughout South and Southeast Asia. Irrigation with untreated effluent has also caused contamination and soil acidification in many areas; in Mongolia, for example, waste disposal and wastewater discharges are the main causes of soil contamination (UNDP 2000).

Actions taken to address soil contamination include Japan's Agricultural Land Soil Pollution Prevention Law which, as well as placing restrictions on contaminating activities, has also instigated remedial projects. By 1999, remedial projects for 79 per cent of the total polluted land area (7 145 ha) had been undertaken (MoE Japan 2000). In the Republic of Korea, the Ministry of Environment established a Soil Contamination Monitoring Network in 1996 to prevent soil contamination adjacent to mines, refineries, military bases, oil storage facilities and waste landfills (Shin-Bom 1996). Australia now has a nationally consistent approach to the assessment of site contamination through the National Environmental Protection Measure (NEPM) for the Assessment of Site Contamination (NEPC 2001).

Many of the failures of physical responses to land degradation problems have stemmed from the competing influences of fiscal and market incentive programmes. The underpricing of resources and subsidization of agricultural inputs such as fertilizers have played important roles in maintaining pressures on land. A major policy failure leading to land degradation is insecure land tenure although in many cases even ownership is insufficient to ensure the sustainable use of land because population pressures have led to the fragmentation and overexploitation of land holdings. Competing economic and environmental policies have also influenced land use practices in New Zealand. Government subsidies in the 1970s and 1980s resulted in the conversion of large areas of forest and woodlands to pasture and crops, dramatically increasing the risk of erosion in these areas. However, since the removal of these subsidies in the 1980s, large areas of marginal pasture on steep land have been allowed to regenerate to scrub and native forest, reducing the risk of erosion (MoE New Zealand 1997).