Introduction

Soil and water, with the functions they have and the nutrients they carry, underlie all agriculture. Soil is the indispensable resource for adequate crop production: it is the medium in which plants grow, and it contains or stores nutrients essential for life. Water is needed for biosynthesis, a process for which sunlight normally provides the energy.

But soil and water is also a fragile combination and in some places are threatened. In 1995, there were, worldwide, about 5.8 million square kilometers of land that had been degraded by deforestation, 6.8 million degraded by overgrazing, 1.37 million degraded for fuel wood, 5.5 million degraded by agricultural mismanagement and 195,000 degraded by industry and urbanization (FAO, 1996). The amounts of phosphates, sediments, heavy metals and pesticides found in watercourses also raise concerns about the dangers to human, terrestrial, and aquatic life. The extent of soil degradation and water contamination is, in many cases, dangerously advanced, and if actions for better soil and water conservation are not taken rapidly, the planet will experience great difficulty in being able to support the still growing human population.