Assessing and Managing Agricultural Nitrogen Losses to the Environment.- I. Introduction.- II. Contributions to N Input.- III. N Loss Processes.- IV. Practices to Ameliorate N Losses or Increase N Use Efficiency.- V. N Research Tools.- VI. Research Needs.- References.- Assessing and Modifying Ca and Al Levels in Acid Subsoils.- I. Introduction.- II. Soil Al and Plant Response.- III. Ca Deficiency and the Ca/Al Relationship.- IV. Ca and Al in Acid Subsoils.- V. Conclusions.- References.- Application of Electron Spin Resonance (ESR) Spectroscopy in Soil Chemistry.- I. Introduction.- H. Basic Principles and Methodology of ESR Spectroscopy.- III. Organic Free Radicals in Humic Substances.- IV. Free Radicals in Humic Substance-Herbicide Interactions.- V. Metal-Humic Substance Complexes.- VI. Metal and/or Organic Interactions with Oxides, Hydrous Oxides, and Clay Minerals.- VII Summary and Conclusions.- VIII. Recommendations for Future Work.- References.- Microelectrophoresis Applied to the Surface Chemistry of Clay Minerals.- I. Introduction.- II. Quantitative Applications.- III. Qualitative Applications.- IV. Conclusions.- References.- Applications of Luminescence Spectroscopy to Studies of Colloid-Solution Interfaces.- I. Introduction.- II. Fundamental Principles.- III. Applications of Fluorescence to Colloidal Systems.- IV. Conclusions.- References.
The study of soils today has taken on increased importance because a rapidly expanding population is placing demands on the soil never before experienced. 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. 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. Until recently, sustainability was seldom, if ever, mentioned in agricultural literature. Now, it is one of the most widely used terms. The high costs ofirriga tion development, escalating energy costs during the 1970s, public concern over potential negative impacts of fertilizer and pesticides on water supplies, soil ero sion, soil compaction and salinity problems, and other concerns have caused many people to question whether many of the present agriculture systems can be sustained. As a result, soil science is beginning to focus more on sustaining the resource base.
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