摘要:

AbstractThe effects of planting cereal or leguminous crops in rotation with irrigated cotton (Gossypium hirsutum L.) on the properties of cracking clay (swelling) soils in the Macquarie and Namoi Valleys of New South Wales, Australia were evaluated during the summer of 1992–3. The observations were made on commercial farmers' fields. The soil properties evaluated were the particle size distribution, the dispersion index, the plastic limit, the percentage of coarse (particle diameter 212–2000 μm) and fine (particle diameter 53‐212 μm) particulate soil organic matter, soil respiration rate, soil reactivity, soil aggregate density, pH, nitrate‐N and exchangeable Ca, Mg, K and Na. In general, the planting of rotation crops decreased the dispersion index, plastic limit and soil aggregate density, and increased the amount of coarse particulate organic matter. Planting rotation crops also resulted in significantly higher clay and lower silt contents in the Macquarie Valley, and significantly higher soil respiration in the Namoi Valley. Soil pH, nitrate‐N and exchangeable cation concentrations were not significantly affected by planting rotation crops in the Macquarie Valley, whereas exchangeable Na was increased in the Namoi Valley. The retention of crop residuesin situ, compared with burning crop residues, decreased the dispersion index, plastic limit and aggregate density, and increased the amount of coarse particulate soil organic matter at all measured depths of the Macquarie Valley. The retention of crop residues in the Namoi Valley decreased the plastic limit and dispersion index only in the 0–50 mm depth range, whereas burning crop residues increased exchangeable K at all depths. In general, planting rotation crops and the retention of crop residues had greater beneficial effects on the soil physical properties in the Macquarie Valley than in the Namoi Valley, and in the topsoil compared with the subsoil. These differences are attributed to a shorter rotation interval in the Namoi Valley, smaller amounts of coarse particulate soil organic matter in the subsoil, and differing soil types in the two valleys. In the Namoi Valley the coarse organic matter produced by leguminous crops appeared to be more effective in promoting structural stability than that from non‐leguminous crops, although no such difference was observed in the M

ISSN:1085-3278    

DOI:10.1002/ldr.3400050102

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractVegetation is a major control of dune surface activity. To assess the effect of removing vegetation from otherwise largely inactive sand‐dune surfaces, two field experiments were undertaken in the southwest Kalahari Desert of southern Africa. In the first, wind velocity profiles were measured on two flat surfaces, one vegetated and one where vegetation had been removed by fire. In the second, levels of dune surface activity were measured on burnt and vegetated sites over a ten week period. The data indicate a striking increase in the near‐surface wind velocity allied to a decrease in shear stress after the destruction of the vegetation canopy as a result of burning, grazing or drought. Measurements on the consequences of such changes in the airflow patterns on dune dynamics suggest a three‐fold increase in dune surface activity after vegetation clearance. The dunes therefore have a staggered response to the contemporary environment, being largely inactive relicts for much of the time, but becoming more active as vegetation is episodically re

ISSN:1085-3278    

DOI:10.1002/ldr.3400050103

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA framework for planning development strategies for sustainable land use in developing countries is proposed based on the carrying capacity concept. The rehabilitation of degraded land includes a stabilization and a restoration phase, with corresponding measures to be taken and funding modalities to be explored. Restoration measures focus on the rehabilitation of ecosystem functions, but are effective only when preceded or accompanied by measures stabilizing exploitation levels. Short‐term benefits are required to ensure local participation, but may be counterproductive when long‐term ecological rehabilitation is the major objective. Incentives are important policy instruments to enhance participation by rural communities in rehabilitation activities. Long‐term economic, ecological and social (humanitarian) arguments, at a scale surpassing the local level, should receive more attention in the process of justifying investments for land rehabilitation. Some criteria and conditions to be met both at a macro‐scale and at the local level are di

ISSN:1085-3278    

DOI:10.1002/ldr.3400050104

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractLand evaluation is an important basis for landscape and land use planning. A framework was developed for land evaluation in an area of severe erosion, focusing on integrative, process and ecological analyses. Two classification systems, soil quality and erosion risk, were combined in the land evaluation framework. The Quanjiagou catchment, with typical loess hill and gully topography, in the loess plateau of China was selected as the study area. A geographical information system (GIS) was used for data storage, analysis and display. The soil quality classification was based on the main characteristics of the soils (soil organic matter, effective depth of soil and soil moisture); four soil quality classes were defined in the study area. Slope, micro‐landform type and the type and processes of soil erosion were integrated to classify the erosion risk. The soil qualities and erosion risk for each site were combined using the GIS to evaluate the suitability of the land for farmland, grassland and forest. By comparing these results with the current land use, measures for better land use and conservation are suggeste

ISSN:1085-3278    

DOI:10.1002/ldr.3400050105

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe semiarid regions of Spain, including the central part of the Ebro River basin, are under threat due to desertification. Severe erosion, as a result of poor land management, has led to degradation of the soil resource, and there is a clear need for quantitative erosion rate data to evaluate the problem. This study aimed to examine the potential for using caesium‐137 to identify the patterns and rates of soil erosion and redistribution within this semiarid environment. Samples for the determination of caesium‐137 were collected from uncultivated slopes and cultivated valley floor sites near the head and outlet of a small representative basin in the Las Bardenas area. The measured patterns of caesium‐137 mobilization, redistribution and export provide a semiquantitative indication of the variation in erosion within the study site. Calibration of the caesium‐137 measurements, taking account of the differing behaviour of radiocaesium on cultivated and uncultivated land, allows estimation of the actual rates of erosion and deposition involved. The results show (1) the erosion rates on the cultivated land (1.6–2.5 kg m−2yr−1) are typically more than five times those seen on the uncultivated land (0.2–0.4 kg m−2yr−1), and (2) erosion on the uncultivated land is significantly less severe at the head of the basin than at the outlet. Study of the vegetation cover suggests that lower growing shrubs and grasses may be more effective in reducing erosion in this env

ISSN:1085-3278    

DOI:10.1002/ldr.3400050106

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400050108

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400050109

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400050110

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400050101

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY