摘要:

AbstractSoil chemical, biochemical, biological and structural properties were measured in two New Zealand loessial soils that were topsoil‐mined 10 and 25 years ago respectively. Measurements at the 10‐year site were compared to some earlier measurements made at this site and the data combined in a chronological sequence for analysis. Topsoil mining had a large, detrimental impact on the soil microbial biomass, the earthworm populations, easily mineralizable N and soil enzyme activities. However, most of these properties substantially recovered, to 80‐90 per cent of the levels in unmined soils, within 10‐25 years of restoration under pasture. In contrast, while total soil C and N were less affected by topsoil mining, their recovery was much slower. Stabilities of macro‐aggregates of soil had fully recovered within 10‐25 years after topsoil mining. The apparent changes in all the measured properties between 10 and 25 years of restoration were small in comparison with changes between 0‐10 years of restoration after topsoil mining. The total C content of both soils under pasture appeared unlikely to attain the levels present in unmined soils. In soils undergoing restoration, the ratio of microbial C/total soil C may be a useful index of soil ‘biological stability’. Sulphatase activity may reflect the recovery of p

ISSN:1085-3278    

DOI:10.1002/ldr.3400010202

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractFour pedons of Arenic/Grossarenic Paleustalf (Denteso Series), in the Volta Lake drawdown area in Northern Ghana, were described and sampled just before seasonal floodings commenced in the area. After 5 years of periodic flooding the soils were re‐examined and sampled. Soil properties required for soil classification, including the clay mineralogy, of both the pre‐flooding and the post‐flooding samples were determined. One of the main objectives was to identify changes in soil properties which result from the periodic flooding.X‐ray diffraction (XRD) indicated that before flooding the main clay minerals of the Denteso were kaolinite and smectite, and there were also some mica and quartz in the total clay fraction. Comparison of the pre‐flooding with the post‐flooding data revealed that practically all the smectite disappeared from all the three sampled pedons that were flooded for 5 to 20 weeks during each flood cycle, while the smectite persisted in the non‐flooded pedon. With the disappearance of the 2 : 1 lattice clays there occurred a considerable decrease in cation exchange capacity (CEC) and in base saturation of the flooded pedons ranging from 0.04 to 3.63 cmol kg−1. Also, there was an increase in pH by 0.4 to 1 unit in most horizons of the flooded pedons in spite of the general decrease in base saturation. These changes in CEC, base saturation and pH support the XRD evidence that the seasonal floodings caused pedochemical weathering of the smectite in this loamy sand soil at a very fast rate during the 5 year period and this had resulted in the lowering of the buffering capacity and a general impoverishment of

ISSN:1085-3278    

DOI:10.1002/ldr.3400010203

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractCommunal rangeland management policies in Botswana and Zimbabwe are based on incorrect technical assumptions about the stability of semiarid rangeland, the nature of rangeland degradation, and the benefits of destocking. Consequently, inappropriate policies, stressing the need to destock and stabilise the rangelands, are pursued. Acknowledgement of the great instability but intrinsic resilience of rangeland would encourage the Governments to more favourably regard the opportunistic stocking strategies of the agro‐pastoralists of the Communal Areas. However, degradation of rangelands is occurring, although at varying rates. This justifies the promotion of a ‘tracking strategy’, in which livestock densities are encouraged to follow, more closely that at present, variations in rainfall.The establishment of grazing territories controlled by specific ‘communities’ may be a prerequisite for the promotion of the tracking strategy, and for communal rangeland management and improvement. However, the establishment of such territories must take into account social equity, institutional problems and transaction costs, as well as spatial and temporal variation in rangeland

ISSN:1085-3278    

DOI:10.1002/ldr.3400010204

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractA soil organic matter turnover model has been developed to analyse soil carbon (soil organic‐C) loss caused by organic matter decomposition and rainfall erosion in soils used for permanent cultivation. It has been used to build up model profiles of five soils, one occurring in temperate and four in tropical regions, on the basis of estimates for ‘natural’ organic matter input. Organic matter input data for different systems of cultivation were used to model the long‐term decomposition of soil organic‐C in these model profiles. The modelling results show that soil organic matter decomposition in the tropics is three to four times faster than in temperate regions, and that there is a marked influence of soil type and soil climate. Simulated losses of organic‐C in the tropical soils, not accounting for erosion are 31 to 50 per cent after 50 years and 43 to 63 per cent after 100 years of continuous cultivation. The simulated loss of soil organic‐C when rainfall erosion is also allowed for is 40 to 80 per cent. Erosion caused an extra loss of at least 7 per cent after 100 years. The initial input of charcoal from forest burning is lost through erosion at a rate of 50 to almost 100 per cent, depending on the severity of erosion. The sensitivity of modelling results to variations in input data was also analysed. The losses of soil carbon were also used to calculate the global flux of CO2from soils. Soils are probably a small but not negligible

ISSN:1085-3278    

DOI:10.1002/ldr.3400010205

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractNinety per cent of the sediment load of the Yellow River, the world's muddiest river, comes from the loess plateau region in the middle course of the river. Control of this sediment supply is essential to avoid the danger of flooding in the lower reaches on the South China Plain. Since 1971, sediment loads entering the lower reaches have decreased, by 20 per cent as a result of lower precipitation, and by 27 per cent through soil conservation works and reservoir construction. Reductions in erosion can be obtained by restraining the formation of overland flow through promotion of an effective vegetation cover and elimination of the soil surface cover to encourage infiltration. Reservoir operation is a key to control of sediment movement through tributaries and along the main river. Water demands often conflict with sediment control, and, as a consequence, reservoir operation systems have changed several times in the past decade. The possibility of a further reduction in the sediment load of the Yellow River exists, but much depends on how rapidly control of grazing and deforestation leads to the establishment of plant cover on the loess plateau.

ISSN:1085-3278    

DOI:10.1002/ldr.3400010206

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

摘要:

AbstractCalls for sustainable development have emerged largely because of the failure of technology‐focused, production‐orientated development policies to address the acute rural poverty and deteriorating environments of much of the Third World. Increased agricultural production through greater commercialization has a mirror image of decreasing incomes for the rural poor as market penetration undermines the viability of traditional production systems. These production systems are geared to minimizing risk through the harnessing of the full range of local resources, both private and communal, to produce goods for both the market and home consumption. The need for policies which strengthen traditional production systems is argued through a detailed case study of Dominica, in the Caribbean. The complexity and diversity of what is often considered a single‐crop (bananas) agricultural system is demonstrated by looking at a number of localities in different parts of the Island. The example of Dominica is used to argue for policies which, in the words of Robert Chambers, (1983), … ‘put the last first’. Such policies should strengthen existing diversity in the agricultural system through initiatives which give local farmers greater control over the planning and implementation of interventions. The sophistication of local technical knowledge is stressed, as is the need to integrate this knowledge with the technical expertise of outside pr

ISSN:1085-3278    

DOI:10.1002/ldr.3400010207

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400010209

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400010201

出版商:John Wiley&Sons, Ltd.    

年代:1989

数据来源: WILEY