ABSTRACT
After 30 years of unquestioned success, agriculture is now facing important problems. In developed countries, huge increases in productivity have accompanied a severe depletion of “soil quality” in terms of resistance to erosion, organic contents, and concentrations of heavy metals and pesticide residues. In developing countries, intensification has been less success ful due to socio-economical limitations. Nonetheless, traditional practices do not conserve the quality of soils: stocks of organic matter are rapidly depleted and erosion pulls fine particles out of the surface horizons. In a context of increasing population pressure, this degradation of soils results in many social and environ ment problems (Eswaran 1994).
