This paper examines soil and land degradation. It describes basic processes and factors responsible for degradation, illustrates the cause-effect relationships and differentiates between natural and man-induced regressive effects. The 'critical limit' concept is described in terms of properties beyond which the soil will not support an economically-viable agriculture. This paper is not an exhaustive literature review but emphasizes the scientific principles involved and highlights natural against man-induced processes. Important natural processes are: laterization, hard-setting, fragipan and clay pan formation, and geologic erosion. In comparison, man-induced processes consist of: soil compaction, accelerated erosion, desertification, salt accumulation and leaching and acidification. One of the principal constraints is the problem of data reliability. A reliable database and precise criteria are definitely lacking and hinder the assessment of the extent, type and degree of soil degradation and establishing the cause-effect scenario. Improving our database is, therefore, of a high priority if we are to adopt land use policy for sustainable soil management and long-range resource management. Also outlined, are vital research and development strategies. Judicious resource management policy should emphasize managing prime agricultural land to produce to its maximum potential so that there is no need to cultivate marginal and easily-degraded fragile ecosystems. A strict code of conduct is needed for utilizing marginal/fragile lands. Methods of restoring the productivity of degraded lands must be researched so as to minimize the need to clear and develop new lands.
A silty mantle on the upper Eastern Shore of Maryland was studied to determine its origin and characteristics. Thickness of the silts was studied by selecting traverses in an east‐west direction from the Chesapeake Bay and also scattered borings between traverses. These deposits are believed to be loess; they are characterized by 50 to 75% silt‐sized particles. The material is also carbonatefree, nonstratified, and yellowish brown in color. In addition, the silty mantle shows a reduction in thickness and particle size with increasing distance from the Chesapeake Bay, which was the probable source area. In areas of thin loess (< 90 cm), increasing amounts of sand were apparently incorporated into the loess at the time of deposition. Based on 14C date of a 11A1b horizon of a buried paleosol below the loess, deposition of the silts took place after 10,520 ± 240 years B.P. Profile characteristics of soils developed in the loess show moderately well expressed argillic horizons with the soil in this study having an increase of 9% clay from the A to the B2t horizon or a B2t/A clay ratio of 1.65.
Soil is fragile and nonrenewable but the most basic of natural resources.It has a capacity to tolerate continuous use but only with proper management. Improper soil management and indiscriminate use of chemicals have contributed to some severe global environmental issues, e.g., volatilization losses and contamination of natural waters by sediments and agricultural fertilizers and pesticides. The increasing substitution of energy for labor and other cultural inputs in agriculture is another issue. Fertilizers and chemicals account for about 25% of the production energy investment in agriculture. An additional 60% is accounted for by machinery, gasoline, electricity, and power-related inputs. Fertilizer additions to cropland are not utilized fully and significant amounts, depending on conditions, are either lost in surface runoff or leached into the ground water. The annual discharge of dissolved solids from agricultural lands to the waterways in the USA is substantial. The increasing use of herbicides in agriculture is a threat to the quality of surface and ground water, although this threat is dependent upon both the chemistry of the compound and the ecosystem in which it is used. Especially within the Third WorM, development of an environmental ethic and environmental laws have not kept pace with the increase in pesticide use. Above all is the severe and global problem of soil degradation currently occurring at the rate of five to seven million hectares per year. The policy and moral aspects of these issues are discussed.
More than a half‐million hectares of the moderately well‐drained Canfield soil and its toposequence members occur in northeastern Ohio and northwestern Pennsylvania. These fragipan soils derived from low‐lime glacial till are intensively used for both agricultural and urban purposes. Because this soil is being used for a long‐term study of the disposition of strontium‐90 under natural conditions and because its classification was unconfirmed, 18 profiles from the Ohio Agricultural Research and Development Center at Wooster were described and characterized. The soil profile tended to be bisequal with a moderately well‐developed, loam fragipan occurring at an average depth of 45 cm. The bulk density of the fragipan centered on 1.7, with coarse fragments occupying about 12–16% by volume. The Canfield series was found to contain an argillic horizon above the fragipan and was classed as an Aquic Fragiudalf assigned to the fine‐loamy, mixed, mesic family. The fragipan controls the hydraulic conductivity of this soil, resulting in lateral movement of percolating water across the fragipan surface equivalent to about 30% of the total precipitation. The quantity of subsurface runoff which must accrue from the long slopes, which sometimes exceed 300 m, poses a major problem for the use and management of this soil.
The evolution of agriculture within the last 11,000 yr marked the first major inflection point in food yield and changed forever the character of the human condition. The application of technology to agriculture early in the 20th Century induced the next major crop yield inflexion point. Identifying the technological wellspring from which increased rates of productivity will be obtained in the decades ahead is far less obvious than during the last century. The agronomic challenge for the decades to come is to increase productivity per unit of land enough to preclude appropriation of other ecosystems for cropland expansions while simultaneously increasing the efficiency of production inputs, reducing their leakage to the environment, and sustaining the integrity of those ecological processes that undergird these intense biological production systems. Such a goal will require different metrics to measure agricultural sustainability and garner public support, new funding sources, and more holistic institutional arrangements. Agronomists, while playing a major role in meeting this challenge, will not necessarily dominate the agenda.
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