The key to sustaining the soil resource base is to maintain, or enhance, soil quality. Soil quality cannot be seen or measured directly from the soil alone but is inferred from soil characteristics and soil behavior under defined conditions. In essence, the quality of soils is analogous to the health of humans, and just as there is no single characteristic that can be measured to quantify a person's health, there is no single measurement that can quantify soil quality. However, there are certain characteristics, particularly when considered together, that are good indicators. Soil quality, just as human health, can be maintained or enhanced by good management practices; and seriously degraded-sometimes irrevers ibly-with poor practices. Soil quality is also important because it has direct and indirect effects on air quality and water quality. While the enhancement of soil quality does not always assure parallel improvements in the quality of air and, particularly, water resources, this is often the case. However, soil deg radation is invariably accompanied by degraded qualities of both air and water resources. The consensus among many scientists is that the greatest challenge is not increasing production, but preventing serious deterioration of the soil and water resource base so that the production level can be sustained.
Inhaltsverzeichnis
Physical Fractionation of Soil and Organic Matter in Primary Particle Size and Density Separates.- I. Introduction.- II. Soil Fractionation Methodology.- III. Soil Organic Matter (SOM) in Density Separates.- IV. Chemical Characteristics of SOM in Size Separates.- V. Dynamics of SOM in Size Separates.- VI. The Use of Size Separation in Applied Research.- VII. Feasibility of Physical Soil Fractionation in SOM Studies.- References.- Soil Water Repellency.- I. Introduction.- II. The Effects of Repellency.- III. Definition and Measurement of Repellency.- IV. Development of Repellency.- V. Amelioration of Repellency.- VI. Conclusions and Future Research Priorities.- References.- Stem-Nodulating Legume-Rhizobium Symbiosis and Its Agronomic Use in Lowland Rice.- I. Introduction.- II. Diversity of Stem-Nodulating Legumes.- III. Working Definition of Stem Nodule.- IV. Classification of Stem-Nodulating Rhizobia.- V. Infection Process, Nodule Formation, and Fine Structure of Stem Nodules.- VI. Biological Nitrogen Fixation and N Accumulation by Stem-Nodulating Legumes.- VII. Factors Affecting Symbiosis.- VIII. Agronomic Use of the Stem-Nodulating Legumes.- IX. Conclusion and Agenda for Future Research.- References.- Analysis of Lognormal Data.- I. Introduction.- II. Diagnosing Lognormality.- III. Estimating Population Parameters from Sample Data.- IV. Hypothesis Testing.- V. Concluding Remarks.- References.- Nutrient Transformations in Soils Amended with Green Manures.- I. Introduction.- II. Nutrient Contributions by Green Manures.- III. Effect of Green Manuring on Chemical and Electrochemical Properties of Soils.- IV. Nitrogen.- V. Phosphorus.- VI. Potassium, Calcium, and Magnesium.- VII. Sulfur.- VIII. Micronutrients.- IX. Conclusions.- References.
