the soil to sustain food production in the future is unimpaired. This is indeed a mammoth task; a 1977 United Nations survey reported that almost one-fifth of the world's is now being steadily degraded. The diversity of soil makes it cropland necessary for research to be conducted in many locations. There are basic principles, however, that are universal. This, Advances in Soil Sciences, presents clear and concise reviews in all areas of soil science for everyone interested in this basic resource and man's influence on it. The purpose of the series is to provide a forum for leading scientists to analyze and summarize the available scientific information on a subject, assessing its importance and identifying additional research needs. But most importantly, the contributors will develop principles that have practical applications to both developing and developed agricultures.