Soil erosion is a quiet crisis, an insidious, largely man-made disaster that is unfolding gradually. In many places it is barely recognized; the soil moves away in such small increments from day to day that its loss is hardly noticed. Often the very practices that cause the greatest losses in the long term lead to bumper crops in the short term, thereby creating an illusion of progress.
Yet erosion is inexorably undermining the economic security of most countries. The changes it brings are chronic and irreversible: lost land; reduced productivity on farms and in forests; floods; silted harbors, reservoirs, canals, and irrigation works; washed-out roads and bridges; and destroyed wetlands and coral reefs, where myriad valuable organisms would normally breed and prosper.
And erosion is literally costing the earth. The soil it carries off now totals 20 billion tons a year worldwide. That represents the equivalent loss of between 5 million and 7 million hectares of arable land. Some of this loss is alleviated by converting forests into farms, so that erosion indirectly also leads to deforestation.
The problems are worst in the warmer parts of the world. There, swelling populations, poor land management, vulnerable soils, and hostile climates add up to a lethal combination that fosters erosion, bringing with it environmental degradation, falling crop yields, rising deforestation, erratic water supplies, and an ever-expanding prospect of dry and dusty rangelands too lacking in soil for crops or even livestock.
Soil erosion is getting worse. In sub-Saharan Africa, for example, it has increased 20-fold in the last three decades as more and more people are forced to move out of the good bottomlands and onto the fragile hillsides. More than one-third of Africa, for example, is threatened with desertification. The world's forests are disappearing 30 times faster than they are being planted. Hillsides stripped of their protective covering of vegetation are rapidly eroding, depositing huge amounts of silt into downstream reservoirs and river valleys. Floods are becoming more frequent-and more severe.
A few facts demonstrate the crisis:
· Morocco has to install the equivalent of a new,
150-million cubic meter reservoir every year just to keep pace with the sediment
that is filling up its existing dams.
· Zimbabwe, it is estimated, would have to spread US$1.5 billion worth of fertilizers merely to compensate for the natural nutrients now being swept away by wind and rain every year.
· China loses more than 2 billion tons of soil a year, just from the Loess Plateau. Most is deposited in the Yellow River. And it takes 3.5 billion cubic meters of water to flush every 100 million tons of soil to the sea-water that could be used for productive purposes.
· U. S. farmers must add 20 kilograms of nitrogen fertilizer for every centimeter of soil lost per hectare, just to maintain productivity. Indeed, each year the United States loses $18 billion in fertilizer nutrients to soil erosion.
To avert the global environmental disaster being brought on by soil erosion, it is imperative to take action quickly and on a vast scale. Unfortunately, previous efforts to tackle the problem worldwide- especially in the Third World-were rarely successful over any extensive area. For one thing, some of the conventional techniques employed today are enormously expensive. For another, they rarely generate widespread farmer support-indeed, the farmers often object so vehemently that they have to be threatened with fines or prison to assure compliance. And, wherever the farmers are unmotivated, even the most effective systems soon decline and fall into decay and disuse.
It was with this grim scenario in mind that the staff of the NRC became intrigued by the ideas of two World Bank agriculturists, John Greenfield and Richard Grimshaw. These two had an entrancing vision: a little-known tropical grass called vetiver, they proposed, could provide the answer to soil erosion in the world's warmer regions-and it could do so in a way that would appeal to millions of farmers, landowners, politicians, and administrators. In their eyes, local people would at last be motivated to protect their land and therefore create the solution rather than the problem.
Greenfield and Grimshaw's concept, as well as the reasons behind it, are described in the next chapter. Subsequent chapters highlight the findings of the NRC panel, whose task was to assess the underlying truth of the vetiver idea and to project its promise into the future.
Noel D. Vietmeyer Study Director