摘要:

AbstractSoil degradation is usually a complex process in which several features of soil deterioration can be recognized. Soil degradation may lead to the loss of land or soil; limitations to normal soil functions; decrease of soil fertility and ‘productive capacity’.The mainsoil degradation processare: (1) soil erosion by water and wind; (2) Development of extreme soil reaction (acidification; salinization/alkalization); (3) physical degradation (structural destruction; compaction; extreme moisture regime); (4) biological degradation; (5) unfavourable changes in the nutrient regime; (6) decrease of buffering capacity (leading to pollution, toxicity).Soil degradation is not an unavoidable consequence of intensive agriculture and social development. Most of the processes and their unfavourable consequences can be controlled, prevented, eliminated, or at least moderated.A rational strategy of efficientsoil degradation controlshould be based on a system involving the following (consecutive) steps: (a) registration of facts and consequences; (b) analysis of reasons, processes, influencing factors and their mechanisms; (c) determination of the theoretical, real, rational and economic possibilities for control; (d) prediction of the potential impacts of these control alternatives; (e) elaboration and extension of technologies for the optimum alternatives.The present status of soil degradation processes in Hungary is briefly summarized in this paper and the possibilities for control are reviewed, with special regard to soil erosion, salinization/alkalization, acidification and physical degradation (compaction, structure destruction). Based on detailed and comprehensive information on soils (thematic maps of various scales; computerized geographical soil information system) the potential future development of various soil degradation processes is forecast and technologies are elaborated and recommended for use in Hungarian agriculture to prevent soil degradat

ISSN:1085-3278    

DOI:10.1002/ldr.3400010302

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA hydroelectric dam currently under construction is likely to have significant adverse impacts on riparian forest bordering the Turkwel River in northern Kenya. The forest is dominated byAcacia tortiliswhich depends upon river flooding. The River has a seasonal and highly ‘flashy’ flow regime, and floods are vital to recharge the floodplain aquifer. Flood regime, bruchid beetle infestation of Acacia pods, and the role of domestic herbivores in killing beetle larvae and grazing seedlings are important influences on Acacia regeneration. The riparian forest is a vital element in the grazing ecology of Turkana pastoralists, particularly in the dry season and in times of drought. Dam construction threatens the degradation of the forest both through reduced survival of existing trees and reduced regeneration. Such degradation would have serious implications for the Turk

ISSN:1085-3278    

DOI:10.1002/ldr.3400010303

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium‐137 (137Cs) was used to quantify net erosion and net deposition within the landscape over a 30‐year period. Uneroded (native) sites were used to establish the mean background level of137Cs in each of the study areas. The assumption being that agricultural sites with137Cs areal activities greater than the native site were subject to deposition, and sites with137Cs less than the native control site were subject to erosion. A linear proportionality model was used to convert the loss or gain of137Cs to net soil erosion or deposition. Results have indicated that accelerated (anthropogenic) erosion has been commonplace on arable land in Saskatchewan, even on near‐level fields (<1.3 degrees). The net integrated sediment output from the five agricultural fields ranged from — 0.6 t th−1y−1to — 6.8 t ha−1y−1(where negative values represent erosion). What is more alarming is that between 40 and 75 per cent of all sites sampled within individual fields had erosion rates in excess of the generally accepted rate of soil formation (1.0 t ha−1y−1). Also, in one highly eroded field (Crystal Springs medium sloping site) 65 per cent of the sites sampled exceeded the upper tolerable erosion rate of 11.0 t ha−1y−1. These results indicate significant degradation of the non‐renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a ‘bare’ state and repeatedly tilled every second or third year. During a fallow period, or prior to crop emergence during a cropping year, fields are subject to wind and water erosion. On near‐level fields wind would be the dominant transport agent, while on sloping fields inter‐rill and rill erosion would be the primary forces of erosion. It is suggested that the appropriate conservation farming response would be to increase application of surface mulches and possibly to decrease the frequency of summer fallowing. Without such efforts long‐term sustainable agricultural production in the Prairies of Canada is conside

ISSN:1085-3278    

DOI:10.1002/ldr.3400010304

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractTemporal and spatial changes in land use, vegetation cover, deforestation and reforestation in the Zambian Copperbelt were studied using a combination of aerial photograph analysis, literature review and inquiries among relevant government institutions.The study showed that between 1937 and 1984 loss of natural woodlands in the Copperbelt of Zambia (total area of Copperbelt: 9,615 km2) amounted to 41 per cent woodland area (8,419 km2). The major causes of this deforestation are woodfuel collection (for firewood and charcoal), cultivation and replacement of natural woodland with forest plantations. These accounted for 38 per cent, 37 per cent and 15 per cent of the total deforestation, respectively. Before 1962 the copper mining industry used large quantities of firewood to generate electricity and this resulted in the loss of 150,413 ha of woodland between 1937 and 1961. When the mining industry switched to hydroelectricity, urban households became the major users of woodfuel. The urban population in the Copperbelt increased from 0.412 million in 1960 to 1.400 million in 1984 and its consumption of woodfuel led to the deforestation of at least 89,436 ha between 1962 and 1984.Deforested areas are left to regenerate naturally. However, due to poor management about 34 per cent of the area deforested before 1962 has failed to regenerate. Although 50,200 ha have been reforested with exotic trees, only 5,020 ha of this is on land previously deforested. Thus only about 10 per cent of reforestation efforts have contributed to the rehabilitation of damaged land. Ninety per cent of the reforestation has actually replaced standing indigenous woodland.Uncontrolled bushfires have destroyed forest plantations and have also caused the failure of woodland regeneration in deforested areas. These observations indicate that if forest resources in the Copperbelt of Zambia are to be properly managed it will be necessary:1to effectively regulate land use changes and;2to control bushfires.

ISSN:1085-3278    

DOI:10.1002/ldr.3400010305

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractLand degradation in the middle and upper Yangtze has caused loss of cultivable land, sediment deposition in reservoirs and changes in the runoff: sediment yield relationships of major tributaries. The Jialin River and the Dukou‐Pingshan sector of the Jingsha River together contribute over 75 per cent of all the sediment carried by the Yangtze at Yichang. As the Jialin catchment has the highest rates of erosion per unit area, high sediment discharges from that river exert a major influence on peak summer sediment discharges on the Yangtze. Even though land degradation is increasing in severity, there is no clear overall pattern or trend in variations in sediment yield since 1950. Some tributaries are affected by major reservoir construction and soil conservation works, others are no

ISSN:1085-3278    

DOI:10.1002/ldr.3400010306

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400010307

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400010308

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400010301

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY