ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Soil science has evolved along two tracks. The agricultural research establishment has fostered the trial-and-error empirical approach which has led to great benefits to agriculture but has been less effective at developing soil science as a science. Sub-disciplines of soil science are now moving forward to develop a better fundamental understanding of the many complex processes occurring in the soil. However, we are not effectively weaving the different sub-disciplines together. If we are to develop healthily as an independent science, rather than a highly specialized collection of applied physicists, chemists, and biologists, we need to give more attention to this integration.Soil Science, which has played an important role in bringing our science this far, could play an even more significant role if it elected to undertake this integrative role.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Proposing long-time goals for soil science entails an article of faith, namely, that improvements are both possible and feasible over the long haul. On that basis four goals are proposed as major ones for the coming decades. First, more of the basic principles that underlie the multitude of processes operating in soils must be identified; to that end, a shift will be needed in the current emphasis in soil research: less effort should go into empirical studies. Second, soil scientists must do better than they have to gain the standing in the scientific community as a whole that their subject matter warrants; soil scientists do not have such standing now. Third, more effective links should be forged with professionals in other disciplines whose work depends much or little on soils but who are outside of agriculture; some such links have been developed in the past, but more are needed to make soil science most useful to the public at large. Fourth, the public image of soil needs to be made more accurate.Commonplace as soils are, they are largely taken for granted with little or no appreciation of the complexity of processes operating in the systems. The limited understanding in turn limits possible applications of soil science that would be-useful.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Too little has been written about the contribution to knowledge, and hence to society, arising from the scientific study of the soil. It has failed to excite the same interest, and to command as much expenditure, as for instance the study of the stars, although well into this century the origins and composition of many soils were as much a mystery as were those of the stars.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Soil Scientists today are concerned with the effects of soil management on the total environment. Land use, type of tillage, irrigation practices, and application of pesticides and fertilizers can have far-reaching effects on soil and water quality and the content of “greenhouse” gases in the atmosphere. The need for research on these effects has not lessened the importance of continued research to maintain the capacity of soils for producing food and fiber. Soils must be protected against degradation by erosion, salinity, depletion of fertility, or accumulation of contaminants from various sources. Maintaining the quality of our soil, water, and air resources to meet the requirements of future generations constitutes the environmental challenge to soil scientists.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

The prevalent approach to selection of research topics is haphazard, or—worse—dictated by bureaucratic funding agencies. This paper is a call for an active process of deliberation among scientists (a process of “pre-search”) to help bring to light problems worthy of research that might otherwise be neglected. Several unresolved issues and frontier areas in contemporary soil physics are mentioned by way of example. A warning is sounded against the tendency to follow faddish topics. There is need to redress the growing imbalance between the ease and institutional incentives to publish unsubstantiated theory based on simpler, “purer” systems and the difficult but essential task of carrying out comprehensive experiments on a realistic scale in the field for the purpose of validating theories and models.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

Part I of this paper presents an account of what we know at this time about SOM (soil organic matter). It deals with the distribution and functions in soils of SOM, descriptions of methods of extraction and fractionation, and chemistry of the major components. These include carbohydrates, nitrogenous compounds, organic P and S compounds, and last but not least, humic substances. The latter are discussed in greater detail in terms of analytical characteristics, chemical structure, free radical content, colloid-chemical characteristics, physiological effects, uses, and interactions with metals, clay minerals, and organics (especially pesticides). The second part of this paper focuses on the laboratory of the future and the agenda for the next 75 years. There will be major changes in laboratory procedures from wet chemical to sophisticated instrumental methods, using solid-state samples. Gaps in our knowledge of major SOM components and their interactions with metals, clays, and organics will be filled. Because SOM serves as soil conditioner, nutrient source, substrate for microbial activity, preserver of the environment, and major determinant for sustaining or increasing agricultural productivity, SOM chemists are bound to play an important role in the soil science of the future.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

A chemical model that stresses the role of proton donors in soil genesis is proposed. The model proposes that the abundance, strength, and ability of the conjugate bases to participate in chemical reactions are keys to weathering and pedogenic processes. The study of soil solution has been instrumental in determining the role of proton donors and has led to the development of this chemical model. Conventional pedological investigations only analyze the solid phase and consequently do not allow the identification of the proton donors. Soil-forming processes are defined as a combination of weathering and transportational processes occurring in the absence or presence of living and dead biota. Proton donors initiate weathering reactions and participate in transport of ions released during weathering. While the concept of proton and ligand-promoted dissolution is not new, our recent work with solutions collected from different ecosystems has revealed which acids are important in different soils and throughout the horizons in a given profile. The perspective here illustrates the role of proton donors by describing models of soil genesis.In surveying the proton donors present in the soil, it is recognized that not only is the strength of the acid as indicated by the pKaimportant in weathering reactions but also the ability of the conjugate base to form complexes. On this basis, the acids are classified as weak, strong, and complexing acids. Reactions involving these acids are presented indicating their tendency to cause congruent and incongruent dissolution. The influence of the soil-forming factors (climate, biota, parent material, topography, and time) on the source and distribution of proton donors is presented. Finally, three case studies are presented to reveal how studies involving soil solutions have been used to identify the major proton donors and to determine the present soil-forming processes.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID

摘要:

This paper does not describe the future course of soil science in the tropics. Rather, it is concerned with some soil-related issues that tropical countries will have to face, and resolve, in the short and medium term. The topics chosen for discussion here are deforestation, the resultant degradation of the soil resource, and soil management for continuous crop production, with particular reference to the humid tropics.Tropical forests are being lost at a rate of at least 10 million hectares per annum, most of which occurs through conversion to agriculture. The removal of a vegetative cover, depletion of soil nutrients and organic matter, and accelerated erosion have led to drastic declines in soil productivity. The tropical uplands, into which future expansion of the cultivated area should largely occur, are particularly vulnerable to erosion once their forest cover has been removed. In releasing about a quarter of the global CO2emission to the atmosphere, the large-scale clearing of tropical forests also contributes significantly to the “greenhouse effect”. Another consequence of forest destruction, especially of tropical rainforests, is the loss of biological diversity.Soil-management for sustainable land use is discussed in the context of various cultivation systems. Shifting cultivation is a stable but extensive system of land use, providing for the subsistence of only a few people per unit area of forested land. Because of rising populations and expectations, this traditional farming system is being increasingly supplanted by more permanent and intensive methods of cultivation. Nevertheless, by leaving the litter and undergrowth intact during land clearing operations and practicing appropriate post-clearing soil management, continuous cropping could be sustained in lowland areas with relatively deep soils. In the uplands, however, where the soils are often shallow and easily erodible, agro-forestry appears to be a better alternative in terms of soil conservation.The development and implementation of sustainable farming systems in order to arrest, if not reverse, soil degradation must rest on the willing cooperation of the people involved. Soil conservation programs should not only be acceptable to, but also be compatible with the socio-economic aspirations and conditions of the local community.

ISSN:0038-075X    

出版商:OVID    

年代:1991

数据来源: OVID