Advances in Soil Science

From the beginning of agriculture until about 1950, increased food production came almost entirely from expanding the cropland base. Since 1950, however, the yield per unit of land area for major crops has increased dramatically. Much of the increase in yields was because of increased inputs of energy. Between 1950 and 1985, the farm tractor fleet quadrupled, world irrigated area tripled, and use of fertilizer increased ninefold. Between 1950 and 1985, the total energy used in world agriculture increased 6. 9 times. Irrigation played a particularly important role in the rapid increase in food production between 1950 and 1985. The world's irrigated land in 1950 totaled 94 million hectares but increased to 140 million by 1960, to 198 million by 1970, and to 271 million hectares in 1985. However, the current rate of expansion has slowed to less than 1 % per year. The world population continues to increase and agricultural production by the year 2000 will have to be 50 to 60% greater than in 1980 to meet demands. This continued demand for food and fiber, coupled with the sharp decline in the growth rate of irrigation development, means that much of the additional agricultural production in future years must come from cultivated land that is not irrigated. Agricultural production will be expanded in the arid and semiarid regions because these regions make up vast areas in developing countries where populations are rapidly rising.

Improving the Sustainability of Dryland Farming Systems: A Global Perspective.- I. Introduction.- II. The Concept of Sustainability.- III. Dynamics of Soil Productivity.- IV. Opportunities and Limitations.- V. Perspectives and Strategies.- References.- Agroclimatology of Semiarid Lands.- I. Introduction.- II. Climatic Resources.- III. Soils.- IV. Agroclimatic Indices.- V. Limitations.- VI. Research Needs.- References.- Conservation Tillage Systems.- I. Introduction.- II. Conservation Tillage Equipment.- III. Weed Control.- IV. Water Infiltration, Evaporation, and Conservation.- V. Crop Growth, Yields, and Water Use.- VI. Soil Erosion and Environmental Quality.- VII Insects, Plant Diseases, and Other Pests.- VIII Soil Properties.- IX. Economies.- X. Summary and Conclusions.- References.- Tillage and Residue Management Effects on Soil Organic Matter Dynamics in Semiarid Regions.- I. Introduction.- II. Characteristics of Semiarid Regions.- III. Properties and Factors Affecting Soil Organic Matter.- IV. The Effect of Residues on Soil Structure.- V. Tillage and Residue Management Effects on Soil Organic Matter and Nutrients.- VI. Tillage Strategies for Improved Management of Organic Matter and Plant Nutrients.- VII. Cropping Methods for Maintaining Soil Organic Matter and Nutrients in Semiarid Areas.- VIII. Summary and Conclusions.- References.- Tillage Systems and Equipment for Dryland Farming.- I. Introduction.- II. Factors Affecting Selection of Tillage System.- III. Tillage Systems.- IV. Summary and Needs.- References.- Fertility Management and Nutrient Cycling.- I. Introduction.- II. Principles Relating Water and Nutrient Availability.- III. Water Deficits.- IV. Management Practices.- V. Conclusions.- References.- Water-Use Efficiency.- I. Introduction.- II. Seeding Rate and Planting Geometry.- III. Crop Calendars.- IV. Crop Selection and Germplasm Enhancement.- V. Water Management.- VI Soil Fertility.- VII. Research Needs for Improved Water-Use Efficiency.- References1.- Water Erosion and Water Quality.- I. Introduction.- II. Impacts.- III. Prediction.- IV. Research Needs.- V. Summary.- References.- Wind Erosion: Mechanics, Prediction, and Control.- I. Introduction.- II. Basic Wind Erosion Process.- III. Extent of Problem.- IV. Deposition of Eroded Material.- V. Impact on Soil Productivity.- VI. Wind Erosion Control.- VII. Conclusions.- References.- Methods for Removing Spatial Variability from Field Research Trials.- I. Introduction.- II. Experimental Design.- III. Methods of Statistical Analysis.- IV. Explicit Trend Analysis and Removal.- V. Comparison of Methods.- VI. Summary.- References.- Diseases Caused by Root-Infecting Pathogens in Dryland Agriculture.- I. Introduction.- II. Etiology.- III. Epidemiology.- IV. Host Range and the Effects of Crop Rotations.- V. Tillage and Crop Residue Management.- VI. Strategies and Approaches to Economic Control.- VII. Research Needs.- VIII. Epilog.- References.- The Role of Soil Biodiversity in Sustainable Dryland Farming Systems.- I. Introduction.- H. Diversity/Erodibility Relationships.- III. Early Bioindicators of Soil Degradation.- IV. Measurements to Characterize Biodiversity.- V. Implications for Conservation of Marginal Lands.- VI. Future Research Needs.- References.- Managing Crop Residues to Optimize Crop/Livestock Production Systems for Dryland Agriculture.- I. Introduction.- II. Available Water and Crop Yields.- III. Value of Crop Residues for Water Conservation.- IV. Effect of Surface Residue Management on Crop Yields.- V. Value of Crop Residues for Erosion Control.- VI. Progress with Residue Management Systems.- VII. Conservation Management and Water Quality.- References.- Agroclimatic Approaches for Improving Agricultural Productivity in Semiarid Tropics.- I. Introduction.- II. Agroecological Features of the Semiarid Tropics.- III. The Indian SAT.- IV. The Sahelian SAT.- V. Botswana SAT.- VI. Summary and Conclusions.- References.- An Economic Analysis of Farm Management Practices and Improved Technologies in the Sahel.- I. Introduction.- II. Farming Conditions in Mali.- III. Technological Options for Dryland Farming.- IV. Soil, Water, and Crop Management Case Studies.- V. Case Study Results.- VI. Conclusions.- References.- Use of Crop Simulation Models in Dryland Agriculture.- I. Introduction.- II. Evaluation of New Crops in Australia.- III. Application of Grain Sorghum Simulation Models in Central Texas.- IV. Future Trends in Model Use.- References.- Strategies for Increasing the Productivity and Stability of Dryland Farming Systems.- I. Introduction.- II. Successful Dryland Regions.- III. Dryland Technologies.- IV. Research and Technology Transfer.- V. Research Needs.- VI. A Strategy for Achieving Improved Dryland Production.- References.