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IntroductionOneofthemajordrawbacksofalleycroppingsystemsinsemiaridlowfertilityconditionsiscompetitionforavailablewaterandnutrients.Competitionistobeexpectedifthetreeandthecrophaveoverlappingactiverootsystemsinspaceandtime.Aknowledgeofthespatialdistr… 相似文献
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D.N. Mungai C.L. Coulson J.K. Ng'' Ang'' A G.W.S. Netondo G.O. Umay C.J. Stigter 《环境科学学报(英文版)》2001,13(3):291-298
IntroductionOnlyabout 2 0 %ofKenya’stotallandareahashighpotentialforagriculturalproduction ,therestbeingaridorsemi arid .TheannualpopulationgrowthrateinKenyaofcloseto 4 %isoneofthehighestintheworld (e .g .UnitedNationsDevelopmentProgramme ,1990 ) .Thissituationhasl… 相似文献
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IntroductionKenya○shighpopulationgrowthratehascreatedpressureonthehighpotentialareas.Thishasresultedinthemigrationofpeopletouncultivated“marginal”landswhichmakeupabout80%ofthecountryandarepredominantlyoflowagriculturalproductivity(Hornetz,1990).These… 相似文献
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After a historical introduction, recent achievements in agrometeorology and their limitations are highlighted. It is then discussed what determines what we do in agrometeorology. It is argued that the needs in the livelihood of farmers should push the scientific support systems and it is exemplified that this is possible. This analysis has serious consequences for science, training, education and extension in agrometeorology. This applies most strongly for developing countries or tropical studies elsewhere. Farmers’ livelihoods should be connected through agrometeorological services. Farmer or Climate Field Schools are introduced as a new approach to do so. Examples from China are given in which such schools or classes could be used. Finally a pilot project approach for agrometeorological services is discussed in which this could be prepared. 相似文献
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IntroductionIntheFifthFrameworkProgrammeoftheEuropeanCommission(EC,1999),under“toolsforsustainabledevelopment”,therewasrecentlyaspecialcallforproposalsfor“Technologiesforsustainableplantandanimalproduction:buildingblocksforimprovement(forsmallscaleorenvir… 相似文献
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We investigated the effects of a warmer climate, and seasonal trends, on the fate of oil spilled in the Arctic. Three well blowout scenarios, two shipping accidents and a pipeline rupture were considered. We used ensembles of numerical simulations, using the OSCAR oil spill model, with environmental data for the periods 2009–2012 and 2050–2053 (representing a warmer future) as inputs to the model. Future atmospheric forcing was based on the IPCC’s A1B scenario, with the ocean data generated by the hydrodynamic model SINMOD. We found differences in “typical” outcome of a spill in a warmer future compared to the present, mainly due to a longer season of open water. We have demonstrated that ice cover is extremely important for predicting the fate of an Arctic oil spill, and find that oil spills in a warming climate will in some cases result in greater areal coverage and shoreline exposure. 相似文献
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Jeremy Wilkinson CJ Beegle-Krause Karl-Ulrich Evers Nick Hughes Alun Lewis Mark Reed Peter Wadhams 《Ambio》2017,46(3):423-441
Renewed political and commercial interest in the resources of the Arctic, the reduction in the extent and thickness of sea ice, and the recent failings that led to the Deepwater Horizon oil spill, have prompted industry and its regulatory agencies, governments, local communities and NGOs to look at all aspects of Arctic oil spill countermeasures with fresh eyes. This paper provides an overview of present oil spill response capabilities and technologies for ice-covered waters, as well as under potential future conditions driven by a changing climate. Though not an exhaustive review, we provide the key research results for oil spill response from knowledge accumulated over many decades, including significant review papers that have been prepared as well as results from recent laboratory tests, field programmes and modelling work. The three main areas covered by the review are as follows: oil weathering and modelling; oil detection and monitoring; and oil spill response techniques. 相似文献
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Stigter JB de Haan HP Guicherit R Dekkers CP Daane ML 《Environmental pollution (Barking, Essex : 1987)》2000,107(3):451-464
One of the sources of trace heavy metal elements in air is emission by the oil industry, either directly through stack emissions from refineries or indirectly from emissions of combustion of hydrocarbons. Emission estimates are based mainly on the trace metal content of the crude oil processed. From a literature study carried out at the beginning of the 1990s it became clear that data on the trace metal content of crudes were scarce and showed a very large scatter. For this reason a measurement programme to assess the occurrence and concentrations of a number of trace metals, i.e. Cadmium (Cd), Zinc (Zn), Copper (Cu), Chromium (Cr), and arsenic (As), in crudes which are regularly processed in the Netherlands, was set up. By drafting strict sampling protocols and by constructing a special sampling device, as many as possible of the additional contamination sources were avoided. The study suggests that sample contamination may explain a significant amount of the scatter and some of the high concentrations reported in the literature for certain metals. The measured variation in the concentrations of Cd, Zn, and Cu is thought to be due to associated water and/or sediment particles from the producing wells or that picked up during transport. The greater consistency in our measurements for Cr and As suggests that these metals are predominantly associated with the hydrocarbon matrix. Based on the results of this work, it can be concluded that emissions of Cd, Zn, Cu, Cr, and As by the oil industry in the Netherlands are most probably significantly lower than hitherto assumed. 相似文献