Potassium Dynamics in Soils.- I. Introduction.- II. General Characteristics of Soil K.- III. Forms of Soil Potassium.- IV. Inorganic and Organic Colloids Important in Potassium Dynamics.- V. Techniques for Measuring Potassium Dynamics.- VI. Equations and Models to Describe Potassium Dynamics in Soils and Clay Minerals.- VII. Effect of Temperature on K Dynamics.- VIII. Dynamics Between Solution and Exchangeable Phases of Potassium.- IX. Kinetics of Nonexchangeable and Mineral Potassium Release.- X. Use of Kinetics for Determining Thermodynamics of Potassium Exchange in Soils.- XI. Summary and Future Research Needs.- References.- Models to Assess the Susceptibility of Soils to Excessive Compaction.- I. Introduction.- II. Definitions.- III. Modeling Laboratory Soil Compaction.- IV. Ease/Susceptibility of Soils to Compaction.- V. Excessive Compaction.- VI. Water Contents and Applied Stresses Not Conducive to Excessive Compaction.- VII. Acceptable Loads Versus Drainage.- VIII. Modeling Field Soil Compaction.- IX. Application of Field Soil Compaction Models.- X. Areas of Future Research.- References.- Sources, Amounts, and Forms of Alkali Elements in Soils.- I. Introduction.- II. Differentiating Characteristics.- III. Geochemistry.- IV. Mineralogy.- V. Soil Content.- VI. Soil Forms.- References.- The Diagnosis and Recommendation Integrated System (DRIS).- I. Introduction.- II. Nutrient Concentration and Aging.- III. DRIS Norms.- IV. Making a Diagnosis: Use of a DRIS Chart.- V. Calculating DRIS Indices.- VI. Nutrient Index Interpretation.- VII. Testing DRIS Norms.- VIII. Comparisons of DRIS and Other Diagnostic Systems.- IX. Effect of Leaf Age and Position on DRIS Indices.- X. Universality of Foliar Norms.- XI. Expansion of DRIS Beyond Nutrient Ratios.- XII. Conclusions.- XIII. References.- Soil-Related Nutritional Problem Areas for Grazing Animals.- I. Introduction.- II. General Considerations of Trace Element Problems in Plants and Animals.- III. Geographical Distribution of Nutritional Problem Areas for Grazing Animals.- IV. General Discussion.- V. Future Outlook.- References.
The world needs for food and fiber continue to increase. Population growth in the developing countries peaked at 2. 4 percent a year in 1965 and has fallen to about 2. I percent. However, in many developing countries almost half the people are under 15 years of age, poised to enter their productive and reproductive years. The challenges to produce enough food for this growing population will remain great. Even more challenging is growing the food in the areas of greatest need. Presently the world has great surpluses of food and fiber in some areas while there are devastating deficiencies in other areas. Economic conditions and the lack of suitable infrastructure for distribution all too often limit the alleviation of hunger even when there are adequate supplies, sometimes even within the country itself. World hunger can only be solved in the long run by increasing crop production in the areas where the population is growing most rapidly. This will require increased efforts of both the developed and developing countries. Much of the technology that is so successful for crop production in the developed countries cannot be utilized directly in the developing countries. Many of the principles, however, can and must be adapted to the conditions, both physical and economic, of the developing countries. This series, Advances in Soil Science.
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