|Food Supply Increasingly Relies on Irrigation|
|Irrigated Land as a Percentage of Agricultural Land, 1961-94|
Source: Food and Agriculture Organization of the United Nations (FAO), FAOSTAT Statistical Database (FAO, Rome, 1997).
Notes: Asia and Europe do not include the countries of the former Soviet Union until 1991.
These losses are predicted to worsen as soil degradation continues. Though the total global harvest may not reflect such losses immediately, they may be noticeable in some areas, especially where degradation is severe and progressing quickly. For example, soil erosion is expected to seriously compromise production in southeast Nigeria, Haiti, and the Himalayan foothills, as well as in some parts of southern China, Southeast Asia, and Central America. Salinization is expected to become a major threat in the irrigation systems of the Indus, Tigris, and Euphrates River basins, as well as in northeastern Thailand and China, in the Nile delta, in northern Mexico, and in the Andean highlands. Nutrient depletion is likely to be a serious problem in large areas of Africa and in a variety of other far-flung locations from Myanmar to the Caribbean Basin .
Yet not all the news on soil degradation is bad. More soil-friendly farming practices that minimize tilling and reduce the erosive potential of the tilling that is done are coming into wider use, are spreading into countries such as Morocco, the Philippines, and Thailand, and are expanding regionally in parts of sub-Saharan Africa and South America. These methods include contour farming, terracing, vegetative barriers, and improved land use practices at the farm and landscape levels. Better water management practices that control salinization and lower the amount of irrigation water needed per hectare are also spreading .
Agronomists are beginning to realize that erosion and allied concerns are not just local problems but threats to entire watersheds; as such, they can be managed most effectively when approached in this way. Until recently, most researchers studied degradation on almost a farm-by-farm basis and failed to see the big picture. Now the big picture is available, literally, through geographic information systems (GIS). These databases integrate huge amounts of information – elevation, cropping practices, rainfall, slope, water flow patterns, and other factors – and construct custom-made maps that depict a watershed or farming region in ways in which it could never be seen before.
Where this technology is available, such information can help farmers manage their effect on the soil by identifying those areas that are most amenable to agriculture, as well as those most prone to damage. Researchers in Honduras, for instance, have used GIS to map the hilly Yoro area, where there is pressure to expand cultivation. As expected, the richest soils and highest productivity occur in the valleys, but the maps make clear that high-quality soils exist on some slopes as well.
Farmers and policymakers can use this information to determine which areas are capable of substantial production with the least environmental harm. Also not to be overlooked are other important techniques to improve soil health including increasing organic content and nutrient cycling, as well as soil conservation through use of biologically intensive management practices such as green manures, cover crops, intercropping, agroforestry, and crop rotation.
References and notes
12. Sara Scherr and Satya Yadav, Land Degradation in the Developing World: Issues and Policy Options for 2020, 2020 Vision Policy Brief No. 44 (International Food Policy Research Institute, Washington, D.C., 1997), p. 2.