Soil erosion

Posted: 13 December 2007

The soil is among our most precious resources, yet we often take it for granted or destroy it by making it susceptible to soil erosion. In the Philippines, for example, 22 provinces had been reported to have "alarming" soil erosion rate. Among those that had been losing their topsoil were Cebu, Batangas, Marinduque, Ilocos Sur, and La Union. This means that 58 per cent of the country's total land area of 30 million hectares is susceptible to erosion.

  • The world loses the equivalent of five to seven million hectares of farmland through erosion each year. This is equivalent to the land area of Belgium and the Netherlands combined.

    An example of soil erosion, Ethiopia© Alberto Conti/IFAD
    An example of soil erosion, Ethiopia© Alberto Conti/IFAD
    An example of soil erosion, Ethiopia© Alberto Conti/IFAD
    Soil experts say there is nothing wrong with normal soil erosion, which is even beneficial to man. But accelerated erosion - usually caused by man himself - is harmful. Soil is lost much faster than it is created through normal geological processes.

    It takes 200 to 1,000 years to form 2.5 cm of rich topsoil. But on the average, farmlands are losing 2.5 cm of topsoil every 16 years, or 17 times faster than it can be replaced.

    "Soil erosion is any nation's enemy - far worse than any outside enemy coming into a country and conquering it because it is an enemy you cannot see vividly," said Harold R. Watson, Ramon Magsaysay award-winning soil scientist. "It's a slow creeping enemy that soon possesses the land."

Counting the cost
  • Studies have shown that as much as 20 percent of eroded materials end up in rivers, reservoirs, and irrigation canals. Siltation also can cause serious damage to coral reefs and coastal fisheries.

  • Water and wind are the most important degradation processes in Asia, according to Frank Dent of the UN Food and Agriculture Organization. "Although the processes are different," he said, "there is a common factor in all man-made erosion - the absence of vegetation to hold and cover the soil."

  • What happens when topsoil is eroded? Authors Lester Brown and Edward Wolf in Soil Erosion: Quiet Crisis in the World Economy, wrote: "The loss of topsoil affects man's ability to grow food in two ways. First, it reduces the inherent productivity of land, both through nutrient loss and degradation of the soil's physical structure. Second, it increases the cost of food production."

    Added the two authors: "When farmers lose topsoil, they can only increase land productivity by substituting energy in the form of fertilizer. Farmers who lose topsoil may experience either a loss in land productivity or a rise in costs (inputs). But if productivity drops too low or costs rise too high, they will be forced to abandon their land."

    A recent study by the Royal Commission on Environmental Pollution concluded that approximately 30 per cent of the world's arable crop land has been abandoned because of severe soil erosion in the last 40 years.

    Brown and Wolf said that the immediate effects of soil erosion are economic but in the long run its ultimate effects are social. "When soils are depleted and crops are poorly nourished, people are often undernourished as well. Failure to respond to the erosion threat will lead not only to the degradation of land, but to the degradation of life itself."

Conservation measures

  • Planting trees along the roadside nearXilinhot as part of Central-Government funded effort  to control dust storms.© US Embassy in China, April 2001
    Planting trees along the roadside nearXilinhot as part of Central-Government funded effort to control dust storms.© US Embassy in China, April 2001
    Planting trees along the roadside near Xilinhot as part of Central-Government funded effort to control dust storms.© US Embassy in China, April 2001
    Among the soil conservation measures are contouring, cover cropping, crop rotation, contour strip cropping, contour buffer planting, terracing, grassed waterways, farm ponds and checks dams, and reforestation.
    Upland farming in Davaousing SALT techniques.© Henrylito Tacio
    Upland farming in Davaousing SALT techniques.© Henrylito Tacio
    Upland farming in Davao using SALT techniques.© Henrylito Tacio
    One of the best examples, which combine various soil conservation measures, is the Sloping Agricultural Land Technology (SALT) of the Mindanao Baptist Rural Life Center in the Philippines. A study showed that a farm tilled in the traditional manner erodes at the rate of 1,163.4 metric tons per hectare per year over a period of six years. A SALT farm erodes at the rate of only 20.2 metric tons per year in the same period.

    The rate of soil loss in a SALT farm is 3.4 metric tons per hectare per year, which is within the tolerable range. Most soil scientists place acceptable soil loss limits for tropical countries like the Philippines within the range of 10 to 12 metric tons per hectare per year.

    "The God-given keys to soil conservation," says Graeme Swincer, a former development adviser to World Vision projects in Asia and the Pacific, "are trees, legumes, earthworms, microorganisms, recycled plants and animal materials like manure.

    "We must strive to protect and enhance the nutrient cycle and to enhance soil fertility," Swincer adds. "This means promoting and implementing sustainable technologies and approaches like alley farming and agroforestry, while eliminating burning and other wasteful practices. It also means supporting reforestation programs and community tree planting efforts and letting land rest once every three or four years."

This section was written by Henrylito Tacio, award-winning Filipino journalist.

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