The study of soils has taken on increased importance because a rapidly expanding population is placing demands on the soil never before experi­ enced. This has led to an increase in land degradation. Land degradation is one of the most severe problems facing mankind. Volume 11 of Advances in Soil Science was devoted entirely to this critical area of soil science. The editors of that volume, R. Lal and B.A. Stewart, defined soil degradation as the decline in soil quality caused by its misuse by humans. They further stated that soil degradation is a major concern for at least two reasons. First, it undermines the productive capacity of an ecosystem. Second, it affects global climate through alterations in water and energy balances and disruptions in cycles of carbon, nitrogen, sulfur, and other elements. Through its impact on agricultural productivity and environment, soil deg­ radation leads to political and social instability, enhanced rate of deforesta­ tion, intensive use of marginal and fragile lands, accelerated runoff and soil erosion, pollution of natural waters, and emission of greenhouse gases into the atmosphere. In fact, soil degradation affects the very fabric of mankind.

Vesicular-Arbuscular Mycorrhizae as Modifiers of Soil Fertility.- I. Introduction.- II. Mycorrhizae.- III. Development of Vesicular-Arbuscular Mycorrhizae.- IV. Root-Soil Interactions.- V. Vesicular-Arbuscular Mycorrhizae and Acquisition of Phospate by Plants.- VI. Vesicular-Arbuscular Mycorrhizae and Nitrogen Nutrition.- VII. Vesicular-Arbuscular Mycorrhizae and the Acquisition of Other Nutrients.- VIII. Vesicular-Arbuscular Mycorrhizae and Plant Growth under Stress Situations.- IX. Managing Vesicular-Arbuscular Mycorrhizae under Natural Conditions.- X. Conclusions.- References.- Argillic Horizons in Modern Loess Soils in an Ustic Soil Moisture Regime: Comparative Studies in Forest-Steppe and Steppe Areas from Eastern Europe and the United States.- I. Introduction.- II. Geographic Comparison of the Forest-Steppe and Steppe Regions of Eastern Europe and the United States.- III. Results.- IV. Discussion.- V. Summary and Conclusions.- Acknowledgments.- References.- Myths and Scientific Realities of Agroforestry as a Strategy for Sustainable Management for Soils in the Tropics.- I. Introduction.- II. Farming Systems Prevalent in the Tropical Rainforest Zone.- III. Need for Introducing Permanently Sustainable Farming Systems.- IV. Alley Cropping.- V. Transfer of Alley-Cropping Technologies.- VI. Research Priorities.- VII. Modus Operandi.- VIII. Linking Training with Research.- IX. Potential of Agroforestry: Myth or Reality.- References.- Land Evaluation: From Intuition to Quantification.- I. Introduction.- II. Historical Perspective.- III. Major Systems and Trends since 1950.- IV. The FAO Framework as a Standard in Land Evaluation.- V. Land Evaluation in Practice: Selected Case Studies.- VI. Yield Estimates and Productivity Ratings.- VII. Use of Models in Regional Land Evaluations.- VIII. Application of Land Evaluation in Land Use Planning.- IX. Conclusions.- References.- Crop Residue Management.- I. Introduction.- II. Grain Yield.- III. Soil Chemical Properties.- IV. Soil Physical Properties.- V. Soil Biological Properties.- VI. Fertilizer Needs of Crops.- VII. Environment.- VIII. Summary and Conclusions.- Acknowledgments.- References.