摘要:

AbstractA high proportion of the soils in the central zone of Santa Cruz, eastern Bolivia, are chemically and physically degraded, with low organic matter and N contents, compacted subsoil layers and a propensity to crusting, hardsetting and wind erosion. The aim of the experiment discussed in this paper was to identify suitable cover crops to be used in combination with subsoiling for the rehabilitation of degraded soils and the improvement of crop yields in eastern Bolivia. Fertilizers were not used because of their high cost. An experiment with a split complete block design, with subsoiling and no‐subsoiling as the main treatments, 14 cover crops and a continuously cultivated soybean/wheat control as the subtreatments, and four replications, was established on a degraded site comprising a mosaic of two compacted siliceous isohyperthermic soils (a coarse loamy Typic Ustropept and a fine loamy Typic Haplustalf). After a two‐year fallow period, the cover crops were incorporated and test crops were sown for five seasons to evaluate the effects of the treatments on subsequent crop yields. Soil samples were taken to measure changes in chemical fertility. The only significant cover crop effect on soil nutrients was an increase in exchangeable K from 0.47 to 0.56 cmolckg−1by Lablab; subsoiling had no effect on chemical fertility. For all treatments there was an average 24 per cent increase in soil organic matter from 13.1 g kg−1at 3 months after cover crop incorporation to 16.3 g kg−1at 19 months after incorporation. No significant differences in total N were found during this period. Test crop yields were not influenced by subsoiling, but were significantly increased by some of the cover crops as compared to the soybean/wheat control during the first three seasons only. Evidence from foliar analysis suggests that the effects of the cover crops on soybean yields were not nutritional and so presumably were physical in nature, whereas the benefits on wheat yields were possibly related to increased N availability.Panicum maximumvar. Centenario andP. maximumvar. Tobiatá gave the highest total yield increases over the first three cropping seasons (101 and 85 per cent, respectively), but these yield increases would not compensate the farmer for the loss of four crop harvests whilst the land was in fallow. These results highlight the difficulties of rehabilitating soil fertility and increasing crop yields through the use of subsoiling and cover crop fallows on compacted, low organic matter soils in easte

ISSN:1085-3278    

DOI:10.1002/ldr.3400050402

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper examines the changes of land uses and landscape patterns in the Ganspoel Catchment, central Belgium, using aerial photography interpretation (photographs taken in 1947, 1969 and 1986). The comparison of land cover areal changes and a transition matrix were used to assess land‐use changes in time and space. The size, fractal dimension and elongation index of patches were quantified for landscape pattern analysis. Grassland increased and farmland decreased in the study area from the 1940s to the 1980s. Forest increased from 1947 to 1969 and decreased from 1969 to 1986. About 49 per cent of the study area experienced changes of land use between 1947 and 1969, and about 36 per cent between 1969 and 1986. The landscape of the study area is more fragmented than it was in the 1940s. Patches have generally increased in number and decreased in size, although the landscape was most fragmented in 1969; fractal dimension of patches are lower, indicating less complex shapes. From 1969 to 1986, 59 per cent of the area of change was on 0–3 degree slopes, and from 1969 to 1986 6.7 per cent was on>8 degree slopes. Changing land uses and landscape patterns may have important ecological implicati

ISSN:1085-3278    

DOI:10.1002/ldr.3400050403

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractIn semiarid regions such as the Maghreb, the pressure on natural resources such as water and soil are increasing. Reservoir sedimentation and soil degradation are basic problems in these areas. The Oued Mina watershed (5000km2) has been chosen by the Algerian Ministry of Agriculture and the Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH for a Technical Cooperation Project to quantify soil erosion and to assess various methods of soil and water conservation at the watershed level. The study area (about 1000km2) is essentially a landscape of ancient dissected plateaux, with badlands as a major feature in some places. Both the agricultural areas and the reservoir, located at the basin outlet, are strongly affected by soil degradation. The climate is semiarid Mediterranean (wet winters), with an average annual rainfall of 300–350mm. Investigations using a large rainfall simulator revealed that soil tillage on marls under semiarid conditions could be an excellent tool to diminish runoff and soil erosi

ISSN:1085-3278    

DOI:10.1002/ldr.3400050404

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe environmental impact of recent changes in land use is assessed in a part of Andalucia, southern Spain, where the deintensification and abandonment of low productivity upland areas is taking place. In the uplands of the Alpujarra, the traditional landscape most at risk is that of the irrigated cultivation terraces. These have often been established centuries ago and rely on water abstracted from streams draining the southern slopes of the Sierra Nevada. The causes of this deintensification include labour shortages, with many Alpujarra municipios reporting population decreases of up to 50 per cent since 1950. Landsat Thematic Mapper digital data from May and August 1992 have been used to identify the various land cover components of the Alpujarra. Ground verification undertaken in September 1992 and April 1993 has confirmed that deintensification of terraced areas around the villages of Trevélez (at 1500m, the highest village in Spain) and Pórtugos (1300 m) can be identified as either grassland or matorral. It is recognized that many classes of land cover are mosaics with several elements at a subpixel scale (e.g. terrace risers with fruit trees). However, the output from image processing has allowed areal estimates of the main land covers representing deintensification within the terraced zone. The pattern of deintensification of terraced land is fairly complex. It can be assumed that all terraces were irrigated and cropped at some stage. Land which is no longer cropped is usually grazed and the invasion of matorral species is common, particularly when irrigation ceases. Unirrigated tree crops and vines are sometimes planted on terraces no longer used for cropping. A model of deintensification of farming on terraced land in the Alpujarra is presente

ISSN:1085-3278    

DOI:10.1002/ldr.3400050405

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractAfter half a century of failed soil and water conservation projects in tropical developing countries, technical specialists and policy makers are reconsidering their strategy. It is increasingly recognised that the land users have valuable environmental knowledge themselves. This review explores two hypotheses: first, that much can be learned from previously ignored indigenous soil and water conservation (ISWC) practices; second, that ISWC can often act as a suitable starting point for the development of technologies and programmes. However, information on ISWC is patchy and scattered. Many ancient, derelict systems are better described than traditions which still persist today. ISWC has been most commonly developed under dry and marginal conditions, and/or on steep hillsides. Sustained population pressure has often tended to stimulate ISWC. There is a need for more incorporation of ISWC into resource conservation programmes: many projects have ignored local traditions to their detriment. It is widely agreed that further study and research on ISWC is required and justified as a logical starting point towards developing adoptable and sustainable soil and water conservation systems for small‐scale farmer

ISSN:1085-3278    

DOI:10.1002/ldr.3400050406

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400050407

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:1085-3278    

DOI:10.1002/ldr.3400050401

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY