Introduction

Soil erosion is a major environmental problem that threatens world food production (UNEP, 1980; Dudal, 1981; Kovda, 1983). In the world today not only is the total population being fed greater than ever before in history, but more humans are malnourished (Swaminathan, 1983). At present, one thousand million people are malnourished and the problem is growing rapidly in severity (Latham, 1984). Many changes have occurred since the early 1900s when most nations were self-sufficient in food. Today, the great majority of the world's 183 nations are major food importers (FAO, 1983), underscoring a growing disparity in food resources (Swaminathan, 1983). The food supply problem has persisted, ‘and in some cases worsened despite an increased pace of development’ (Latham, 1984). Given these ominous trends, the control of soil erosion for a sustainable agricultural system is essential to any program to improve world food security and development.

Adequate food supplies depend on productive land. At present 97% of the food supply comes from land and only 3% from the oceans and other aquatic systems (CEQ, 1980). Hence, we must safeguard the productivity of the land to feed the ever-increasing world population. Just at a time when agricultural efforts are focused on increasing crop yields, land degradation is increasing throughout the world. Global dimensions of land destruction are alarming. About 35% of the earth's land surface is affected (Mabbutt, 1984).